Official Statistics

Influenza in the UK, annual epidemiological report: winter 2024 to 2025

Published 22 May 2025

Main points

The main messages of the 2024 to 2025 season are:

• the season started in the second half of November 2024 with rising influenza A(H1N1)pdm09 activity that peaked just before the start of the new year (2025) and declined after; influenza B activity started in January, leading to a slow decline of overall influenza activity

• overall activity was higher than in the 2023 to 2024 season. Compared to the 2022 to 2023 season the peak was similar in both intensity as well as timing, but the 2024 to 2025 season had a slower overall decline due to the late influenza B activity

• despite overall activity being higher, mortality estimates in the 2024 to 2025 season were lower than in the 2022 to 2023 season

• vaccine coverage in adults was overall lower in the 2024 to 2025 season compared to the 2023 to 2024 season, whereas in children, vaccine coverage overall was similar to the 2023 to 2024 season

• there was moderate estimated vaccine effectiveness (ranging from 30 to 70% depending on age and setting) consistent with estimates from previous seasons

• further modelling estimated that, in England, the vaccination programme averted between 96,000 and 120,200 hospital admissions due to influenza

Disease activity and burden

In the 2024 to 2025 season:

• across nations, cumulative influenza like illness consultation rates in primary care were higher during the 2024 to 2025 season than in the 2023 to 2024 and 2022 to 2023 season

• across nations, cumulative hospitalisation rates for influenza were higher during the 2024 to 2025 season than in the 2023 to 2024 and 2022 to 2023 season

• in England and Scotland, cumulative ICU/HDU admission rates were higher in the 2024 to 2025 season than in the 2023 to 2024 and 2022 to 2023 season

• in England, influenza-attributable excess mortality was estimated at 7,757 deaths, which was higher than in the 2023 to 2024 season (3,555 deaths) but lower than the 2022 to 2023 season (15,867 deaths)

• in England, there were 53 pediatric deaths (influenza mentioned on death certificate or deaths 28 days after a registered positive influenza test), which was higher than in the 2023 to 2024 season (34 deaths) but lower than in the 2022 to 2023 season (72 deaths)

Disease patterns

In the 2024 to 2025 season:

• overall influenza activity across nations started around weeks 47 and 48 2024 (18 November to 1 December) and peaked across nations in week 52 (week commencing 23 December), followed by a few weeks of sharp decline. Overall influenza activity then declined more slowly from end of January and beginning of February and returned to baseline levels at varying times depending by surveillance indicator and nation

• peak activity was higher than in the 2023 to 2024 season, but similar to the 2022 to 2023 season. Overall activity was higher than in both these seasons due to the more gradual decline in overall activity

• the initial rise in activity was driven by influenza A(H1N1) in children and later increased in elderly age groups. Influenza A activity explained peak activity in week 52 2024 (week commencing 23 December) and then declined at a regular rate. There was limited influenza A(H3N2) activity

• influenza B activity started to increase in January 2025 in younger age groups and peaked across nations between weeks 8 (commencing 17 February) and 10 (ending 9 March) of 2025, but with limited activity in elderly age groups

• the differences in activity for influenza A and B by age explain different epidemic patterns across surveillance systems: surveillance systems based on hospital data showed a more monophasic (one regular wave) epidemic because elderly age groups are overrepresented (Figure 25) while community and primary care systems showed more biphasic (pattern showing two or more waves) influenza activity (Figure 16) due to a relatively higher representation of younger age groups

Vaccination coverage

In the 2024 to 2025 season:

• across nations, influenza vaccine coverage in adults in the 2024 to 2025 season was lower than in the 2023 to 2024 season. For children, vaccination coverage was similar comparing to the 2023 to 2024 season. Coverage across nations ranged from 70 to 75% for adults above 65, 25 to 40% for younger adults with clinical risk factors, 45 to 58% for secondary school children, 55 to 68% for primary school children and 30 to 50% for pre-school children

• estimated vaccine effectiveness against primary care influenza attendances ranged from 35% (adults aged 65 and above) to 55% in children. Against hospitalisation, vaccine effectiveness ranged from 38% in adults aged 65 and above to 75% in children aged 2 to 17 years of age

• modelled estimates indicated that, in England, the vaccination programme prevented between 96,000 and 120,200 hospital admissions due to influenza

Community surveillance

Syndromic surveillance

England

In England, national UKHSA real-time syndromic surveillance systems monitor GP in-hours (GPIH) consultations, GP out-of-hours (GPOOH) contacts, emergency department (ED) attendances and NHS 111 triaged calls and online assessments.

The clinical coding and patient healthcare seeking behaviour underpinning these syndromic surveillance systems may change over time and particular caution should be taken in comparing pre-pandemic, intra-pandemic and post-pandemic time periods. For example, both clinical coding and healthcare-seeking behaviour have been affected by the COVID-19 pandemic and therefore syndromic data and trends over the 2019 to 2020, 2020 to 2021 and 2021 to 2022 winter seasons should be interpreted with some caution. Furthermore, during the 2022 to 2023 season, syndromic surveillance data should also be interpreted with some caution due to a ‘group A strep incident’ from week 48 2022. During this incident, national media reports of an increase in severe invasive group A streptococcus (iGAS) disease in children led to changes in healthcare-seeking behaviour across the NHS, particularly in children with iGAS-type symptoms which are likely to have included respiratory presentations of illness, across NHS healthcare services.

111 calls for acute respiratory infection

Weekly NHS 111 triaged calls for acute respiratory infection (ARI) began to increase from week 45 (week commencing 4 November 2024) and peaked in week 52 of 2024 (week commencing 23 December), declining to similar levels as before November 2024 in week 4 2025 (week beginning 20 January) and declining further from week 10 (week beginning 3 March) 2025. Of note, there was a technical issue from Saturday 1 to Monday 3 March, which impacted the availability of NHS 111 triaged call data during week 9 (week commencing 24 February 2025). Overall, during the 2024 to 2025 season ARI calls were slightly higher during the weeks of the highest activity in November and December than in the 2023 to 2024 season, but lower than November and December in the 2022 to 2023 season. Some caution is needed in interpreting attendances around week 52 and week 1 each year as increased calls noted during those weeks may be explained by less availability of primary care services due to bank holidays.

Figure 1. Weekly NHS 111 calls for ARI by season, England, 2021 to 2025

Emergency department attendances

Syndromic surveillance emergency department (ED) attendance data presented here includes 111 EDs (NHS type 1) that reported data throughout the most recent 6 influenza seasons. ED numbers may differ from those presented in previous annual reports, where a different number of EDs were included.

ED ARI attendances increased gradually from around 11,000 attendances per week at the beginning of October 2024, peaked at slightly over 21,600 in week 52 2024, and stabilized back at around 11,000 weekly attendances from week 9 2025 (week commencing 24 February). The ARI syndromic indicator is a composite of respiratory infection diagnoses of which influenza-like illness (ILI, presented below) is one subcomponent. Some caution is needed in interpreting ED attendances around week 52 and week 1 each year as attendances may be impacted by healthcare seeking behaviour during the holiday period and less availability of primary care services due to bank holidays. ARI attendances during November and December in the 2024 to 2025 season were higher than the same months in the 2023 to 2024 season but lower than in the 2022 to 2023 season.

Figure 2. Weekly ED attendances for ARI by season, England, 2020 to 2025

ILI (influenza-like-illness) ED attendances increased from week 47 2024 (week commencing 18 November), peaked in week 52 2024 (week commencing 23 December), with an initial sharp decline until week 2 (week commencing 6 January) 2025 and a more gradual decline thereafter. Some caution is needed in interpreting attendances around week 52 and week 1 each year as attendance levels may be impacted by health seeking care behaviour during the holiday period and less availability of primary care services due to the bank holidays.

Overall, the levels of ED ILI attendances were higher throughout 2024 to 2025 season than recorded during the previous winter (2023 to 2024 season); the first half of the 2024 to 2025 season was very similar to the 2022 to 2023 season, though the peak occurred one week later, however the overall numbers of attendances were higher in 2024 to 2025 due to the slower rate of decrease from week 3 onwards.

Figure 3. Weekly ED attendances for ILI by season, England, 2019 to 2025

Scotland

NHS24 is the NHS phone service for Scotland equivalent to 111 in England, providing a 24-hour hotline available to members of the public who require advice about urgent but not life-threatening medical problems. Data from these calls is recorded by call handlers and stored electronically, including information regarding time of call, geographical location, caller demographics, and call reason.

The proportion of NHS24 calls for respiratory symptoms is calculated through identifying calls with the following call reasons: ‘colds and flu’. Call reason is a free-text field, that is screened for key words used to identify syndromes.

During the 2024 to 2025 season, the percentage of calls for cold and flu gradually increased starting week 46 2024 (week starting 11 November) and peaked at week 52 2024 (week starting 23 December) and gradually declined thereafter.

Figure 4. Weekly percentage NHS24 calls for cold and flu, Scotland, 2021 to 2025

Acute respiratory infection incidents

England

Information on acute respiratory infection (ARI) incidents is based on situations reported to UKHSA health protection teams (HPTs) and entered onto the Case and Incident Management System (CIMS).

These include confirmed outbreaks of acute respiratory infections (2 or more laboratory-confirmed cases of SARS-CoV-2, influenza or other respiratory pathogens) linked to a particular setting, as well as situations where an outbreak is suspected. All suspected outbreaks are further investigated by the HPT in liaison with local partners. Respiratory sampling to identify the virus involved is encouraged, however where clinical-epidemiological risk assessment suggests a higher probability of influenza this may not be done, and antiviral prophylaxis started empirically. Incident reports are manually reviewed during the data cleaning process and assigned to a specific pathogen only if confirmation of a positive virological test can be identified.

Please note that prior to July 2024, ARI incidents were recorded in HPZone, a previous case and incident management system. From July to September 2024, HPTs transitioned to a new system, CIMS. Any interpretation of seasonal and temporal trends since 1 July 2024 should consider the likelihood of differences in reporting of ARI incidents due to this change.

In England, there was a total of 3,332 ARI incidents in closed settings reported between week 40 (week commencing 30 September) 2024 and week 14 (week commencing 31 March) 2025. Virological testing information was available for 2,246 (67.4%) incidents, of which 1,261 (56.1%) were due to influenza, 128 (5.7%) were due to multiple pathogens (at least one of which was influenza) and 857 (38.2%) incidents were due to other pathogens, including 472 SARS-CoV-2 and 179 RSV. In 1,086 (32.6%) incidents, virological testing results were not available.

Of the incidents in which influenza was virologically confirmed, 1,169 (84.2%) were reported from care homes, 63 (4.5%) from educational settings, 109 (7.8%) from hospital settings, 20 (1.4%) from prisons and 28 (2.0%) from other settings. (Table 1).

Table 1. The number of ARI incidents by institution and pathogen, England, week 40 2024 to week 14 2025 [note 1]

Setting	Influenza	Mixed outbreak (with influenza present)	Other pathogens	Not available or not tested	Total
Care home	1,055	114	687	964	2,820
Educational setting	58	5	29	91	183
Hospital	102	7	110	10	229
Prison	19	1	1	2	23
Other	27	1	30	19	77
Total	1,261	128	857	1,086	3,332

Note 1: includes incidents of influenza as well as mixed incidents where at least one of the pathogens identified was influenza.

The majority of reported influenza outbreaks occurred in care home settings, with the highest number in a week observed during week 2 (week commencing 6 January) 2025 (Figure 5).

Figure 5. Number of influenza ARI incidents by week and setting, England, 2024 to 2025 season [note 1]

Note 1: includes incidents of influenza as well as mixed incidents where at least one of the pathogens identified was influenza.

The majority of influenza incidents were virologically confirmed to be influenza A. Most influenza B incidents occurred in the second half of the season (Figure 6).

Figure 6. Number of ARI incidents by week and influenza type in all settings, England, 2024 to 2025 season [note 1]

Note 1: includes incidents of influenza as well as mixed pathogen incidents where at least one of the pathogens identified was influenza.

Scotland

In Scotland, outbreaks are defined where at least two cases (laboratory confirmed and/or suspected) of any ARI within 48 hours in any setting. To be defined as an ARI outbreak, either the pathogen or the scenario entered onto HPZone must be clearly indicative of acute respiratory infection as the type of outbreak.

Across the season, a total of 120 influenza outbreaks were reported. 114 of these were confirmed influenza A, 3 were confirmed influenza B. 114 were reported from care homes. Influenza outbreaks started to increase around week 48 2024 (week commencing 25 November) and peaked during three weeks (similar amount of weekly outbreaks reported): weeks 51 2024 (week commencing 16 December) until week 1 2025 (week ending 5 January) and declined to low weekly amounts (no more than 3 weekly reported outbreaks) from week 6 2025 (week commencing 3 February).

Figure 7. Number of outbreaks by week and influenza type in all settings, Scotland, 2024 to 2025 season

Northern Ireland

Suspected ARI incidents in different settings are notified to the Public Health Agency (PHA) Acute Response Duty Room and recorded in HPZone, a case and incident management system. A confirmed ARI outbreak can be defined as where there are two or more laboratory confirmed cases with onset within a 14 day period, where transmission within the same setting is considered the likely cause.

In Northern Ireland, there were a total of 189 confirmed ARI outbreaks reported to the PHA Acute Response Duty Room from week 40, 2024 to week 14, 2025. Of these, 107 (56.6%) were reported from hospital settings, 77 (40.7%) from residential or care homes and 5 (2.6%) from other settings. Of the 189 ARI outbreaks, 96 were confirmed influenza outbreaks of which 93 were Influenza A (not subtyped), one influenza A(H1) and two influenza B.

Figure 8. Weekly confirmed ARI outbreaks, Northern Ireland, 2024 to 2025 season

Wales

In Wales, information about incidents and outbreaks is taken from the case management system (Tarian) used by Public Health Wales. An incident in this context refers to the way that information is recorded and organised on the case management system. Not all acute respiratory infections affecting two or more people who are linked, for example through attending or being resident in a particular setting, will be recorded as incidents.

Therefore some caution is needed when comparing absolute numbers between nations.

There were a total of 121 ARI incidents reported between week 40 2024 (week commencing 30 September) and week 12 2025 (week commencing 17 March). Of these, 113 (93.4%) were reported from residential or care homes, 3 (2.5%) from educational settings, 2 (1.7%) from hospital settings and 3 (2.5%) from other settings. Virological results indicated that 63 outbreaks involved influenza (including outbreaks with other pathogens detected), 46 outbreaks were due to other viruses and in 12 outbreaks no pathogen was identified.

Figure 9. Weekly ARI incidents reported through Tarian, Wales, 2024 to 2025 season

FluSurvey (internet-based surveillance)

FluSurvey, run by the UK Health Security Agency, is an internet-based participatory surveillance system similar to the InfluenzaNet platform. It was developed to monitor self-reported respiratory symptoms, social contact patterns and health service use in the UK general population in near-real time through a weekly survey of registered participants.

Individuals aged 18 and over can register on the platform and complete a baseline profile questionnaire and weekly symptoms questionnaires on behalf of themselves or members of their household. Participants are sent weekly email reminders inviting them to report any symptoms that they may have experienced and their health-seeking behaviour as a result of their symptoms. For further details see our data quality report: national flu and COVID-19 surveillance.

All 2024 to 2025 season data presented in this report were collected between week 47 (week commencing 18 November) 2024 and week 14 2025 (week commencing 31 March) inclusive, with previous season comparisons including the same reporting weeks (weeks 47 2023 to week 14 2024).

A total of 2,273 participants in the UK enrolled over the course of the season and completed at least one survey with an average weekly participation of 1,428 (62.8%), contributing each week.

Of these 2,273 participants, 64.5% were female and 35.2% were male. Age groups were distributed as follows: 1.5% aged 0 to 17 years, 12.8% aged 18 to 44 years, 41.4% aged 45 to 64 years and 44.3% aged 65 years and above. The majority (2,000, 88%) of participants were resident in England, with 132 participants residing in Scotland, 11 in Northern Ireland and 87 in Wales.

The European Centre for Disease Control (ECDC) ILI case definition of sudden onset of symptoms with at least one of fever (chills), malaise, headache, muscle pain and at least one of cough, sore throat, shortness of breath has been used for reporting. The ILI case definition is derived based on self-reported symptoms and is a broad definition that can include other respiratory illnesses such as COVID-19. The proportion of weekly participants with self-reported ILI episodes peaked in week 52 (week commencing 23 December) 2024 at 7.6% compared to previous season which peaked in week 50 2023 at 5.3% (Figure 10).

Healthcare use is presented as reported use of health services among participants who meet the ILI ECDC case definition. Where use of more than one health care service is reported, secondary care will be indicated over primary care use and physical attendance to primary care will be indicated over use of remote services (for example, telephoning their GP or 111). Among participants who met the ILI ECDC case definition, 16.5% reported contact with health services as a result of their symptoms, compared to 13.7% in the previous season. The most frequently reported contact with healthcare services was a visit to their GP surgery in both seasons (Figure 11).

Figure 10. Weekly ILI incidence per 1,000 participants and their rate of healthcare use reported through FluSurvey, United Kingdom, 2023 to 2025

Figure 11. Percentage of participants reporting healthcare use by type among FluSurvey participants meeting the influenza-like illness case definition, United Kingdom, 2024 to 2025 season

Primary care surveillance

Influenza-like-illness consultation rates

England

Weekly rates of GP consultations for influenza-like illness (ILI) through the RCGP scheme surpassed the 2024 to 2025 season moving epidemic method (MEM) baseline threshold of 8.54 per 100,000 between week 49 (week commencing 2 December) 2024 and week 10 (week commencing 3 March) 2025 (Figure 1). You can find out more about the RCGP scheme in our data quality report.

The 2024 to 2025 MEM medium threshold of 16.27 per 100,000 was crossed in week 51 2024. The ILI rate peaked at 26.6 per 100,000 in week 2 2025. The ILI rates were at the MEM medium threshold levels for 6 weeks (Figure 12).

The ILI rate for the 2024 to 2025 season was similar than that observed in the 2023 to 2024 season up to corresponding week week 46, and higher than that observed in the 2023 to 2024 season between week 47 and week 14. In the 2023 to 2024 season, the ILI rates were above the MEM baseline threshold levels for 7 weeks (Figure 12).

Figure 12. Weekly GP influenza-like illness consultation rates per 100,000 from the RCGP RSC network, England, by season [note 2]

Note 2: MEM thresholds are based on data from the 2016 to 2017 season to the 2023 to 2024 season. Please note the 2019 to 2020, 2020 to 2021 and 2021 to 2022 seasons have been removed.

Scotland

Public Health Scotland reports consultation rates for influenza-like-illness (ILI) in primary care. Typically, around 96% of all practices in Scotland routinely report to PHS on a weekly basis.

GP ILI consultation rates breached the baseline range (11.7 consultations per 100,000 population) in week 50 2024 (week commencing 9 December) and peaked in weeks 51 2024 (commencing 16 December) and week 2 2025 (week commencing 6 January) with a temporary drop in between these weeks. This is likely due to reduced general practice operation hours due to the bank holidays. After this, consultation rates dropped below the baseline threshold in week 5 2025 (week commencing 27 January).

Cumulative GP ILI consultation rates for the 2024 to 2025 season up to week 14 (321 per 100,000) were higher than in the 2023 to 2024 season (240 per 100,000) and 2022 to 2023 season (219 per 100,000)

Figure 13. Weekly GP ILI consultation rates per 100,000 from sentinel GP practices, Scotland, by season

Northern Ireland

PHA reports consultation rates for in-hours influenza or influenza-like-illness (‘flu/ILI’) in primary care. Data with approximately 95% coverage of the Northern Ireland population is auto-extracted weekly from the General Practitioner Intelligence Platform (GPIP).

The GP ILI consultation rate exceeded the pre-epidemic threshold (low activity) of 10.1 per 100,000 population in week 49 2024 (week commencing 2 December) and rates remained above baseline activity for a further 13 weeks before returning to baseline activity in week 10 2025 (week commencing 3 March). The highest consultation rate was reported in week 51 2024(week commencing 16 December)(39.2 per 100,000 population). This peak was earlier compared to the 2023 to 2024 season, but aligned with what was seen during the 2022 to 2023 season.

Figure 14. Weekly GP ILI consultation rates per 100,000 from sentinel GP practices, Northern Ireland, by season

Wales

Consultation rates for influenza-like-illness (ILI) in primary care are calculated using data submitted by sentinel GP practices across Wales, which cover a representative sample of 13% of the population of Wales.

The GP ILI consultation rate crossed the baseline threshold of 11 per 100,000 population in week 50 2024 (week commencing 9 December), peaked in week 2 (week commencing 6 January) 2025 (40 per 100,000) and returned below the baseline threshold in week 9 (week commencing 24 February). Cumulative consultation rates were higher than in both the 2023 to 2024 and 2022 to 2023 seasons.

Figure 15. Weekly GP ILI consultation rates per 100,000 from sentinel GP practices, Wales, by season

General practice sentinel swabbing

Sentinel GP-based swabbing

England

In England, influenza positivity through the GP sentinel swabbing scheme in collaboration with the RCGP was higher overall in comparison with the previous season. Positivity began to increase in week 45 (week commencing 4 November) 2024, compared to week 47 in the 2023 to 2024 season (Figure 16). A total of 15,958 samples were tested between week 40 (week commencing 30 September) 2024 and week 14 (week commencing 31 March) 2025, 2,152 were positive for influenza. During the same period in the 2023 to 2024 season, a total of 17,894 samples were tested and 1,444 were positive for influenza. In the 2024 to 2025 season, influenza A(H1N1)pdm09 accounted for the majority of positive influenza specimens. Among the positive samples for influenza, 52.3% (1,126 out of 2,152) were positive for influenza A(H1N1)pdm09, 12.7% (273 out of 2,152) were positive for influenza A(H3N2) and 30.6% (658 out of 2,152) were positive for influenza B. The number of influenza B detections increased from the start of 2025 (Figure 18).

Figure 16. Weekly percentage testing positive for influenza in GP sentinel practices, England, by season

Broader virological testing is depicted in Figure 17. Influenza comprised 27.0% of the total respiratory pathogens detected in the swabbing scheme. For non-flu pathogens detected through the RCGP sentinel swabbing scheme, enterovirus or rhinovirus (these pathogens are tested together) were the most detected respiratory pathogen (42.0% of total positive specimens). Please note that starting from week 48 (week commencing 25 November) 2024, samples with more than 10 days between the sample collection date and the symptom onset date have been excluded.

Figure 17. Weekly number of samples tested for influenza and other respiratory viruses in GP sentinel practices, England, 2024 to 2025 season [note 3] [note 4]

Note 3: unknown category corresponds to samples with no result yet.

Note 4: reporting of rhinovirus and enterovirus follows a greater lag than for other respiratory pathogens.

Figure 18. Percentage of positive tests for influenza and other respiratory viruses in GP sentinel practices, England, 2024 to 2025 season

During the 2024 to 2025 season, influenza positivity was highest in week 4 (week commencing 20 January) 2025 in those aged under 5 years, in week 8 (week commencing 17 February) 2025 in those aged between 5 and 17 years and in week 52 (week commencing 23 December) 2024 in those aged 18 years and over (Figure 19).

Mainly in those aged under 65 years, there has been an increase in influenza B positivity rates in 2025. Influenza B was predominant in weeks 7 and 8 in those aged under 5 years, between week 4 and week 9 and week 11 and week 14 in those aged between 5 and 17 years and between week 6 and week 14 in those aged between 18 and 64 years (Figure 19).

Figure 19. Weekly percentage testing positive for influenza by type and age group in GP sentinel practices, England, 2024 to 2025 season

In the 2024 to 2025 season, the primary care influenza attendances incidence proxy was higher than that observed in the 2023 to 2024 season, except between week 5 and week 7 2025.

Figure 20. Weekly primary care influenza attendances per 100,000 (proxy) in GP sentinel practices, England, by season [note 5]

Note 5: This is an experimental metric used as a proxy for the incidence of primary care influenza attendances per 100,000 population. This is a composite indicator calculated using the weekly ARI rate per 100,000 population multiplied by the weekly influenza positivity among the ARI presentations. The ARI rate is calculated within the Royal College of General Practitioners Research and Surveillance Centre (RCGP RSC) network of around 2,000 GP practices covering over 19 million registered patients of all ages across England. The influenza positivity is from a subset of the GP practices participate to the virology swabbing surveillance. This approach is described in the WHO pandemic influenza severity assessment (PISA) framework.

Scotland

Community Acute Respiratory Infection (CARI) surveillance is a sentinel community surveillance programme for a range of respiratory pathogens: SARS-CoV-2, influenza A and B, RSV, adenovirus, coronavirus (non-SARS CoV-2), human metapneumovirus, rhinovirus, parainfluenza and Mycoplasma pneumoniae. The programme is open to GP practices across all NHS Boards in Scotland. To become a sentinel site, GP practices voluntarily opt into the CARI programme. The number of participating practices decreased from 180 to 115 over the year, and the number of practices returning swabs each week can vary. Patients in the community who consult a sentinel GP practice who have at least one of four respiratory symptoms (cough, sore throat, shortness of breath or coryza) are tested after consent.

In the 2024 to 2025 season, the percentage of positive tests for influenza increased in week 48 2024 (week commencing 25 November) and peaked in week 52 2024 (week commencing 23 December) at 52%. After two weeks of rapid decline, the rate of decline slowed. As of week 14 2025 (week commencing 31 March), positivity was still 17%, markedly higher than in the 2023 to 2024 season. By the end of the season, there were a total of 3,858 tests positive for influenza.

Figure 22 shows the total counts of positive tests for all tested pathogens, demonstrating that the persistently moderate influenza positivity rate was driven by ongoing influenza B activity. The most frequently detected non-influenza viruses detected were rhinovirus (3,275 samples positive), RSV (1,302 samples positive) and seasonal coronaviruses (1,187 samples positive). The accompanying datafile has more details, particularly for pathogens (Mycoplasma pneumoniae, adenovirus, hMPV and SARS-CoV-2) grouped in the ‘other’ category in Figure 22.

Figure 21. Weekly percentage of tests positive for influenza through CARI, Scotland, by season

Figure 22. Weekly positive test counts for all tested pathogens through CARI, Scotland, 2024 to 2025 season

Northern Ireland

Community sentinel GP practices cover approximately 18% of the population of Northern Ireland. The programme tests for influenza A and B, RSV and SARS-CoV-2 through the opportunistic swabbing of patients who provide consent, and who attend (in person) with ILI, ARI or suspected COVID-19 symptoms. 1,135 swabs were received from week 40 (week commencing 30 September) 2024 to week 14 (week commencing 31 March) 2025. 440 specimens tested positive for influenza, followed by 65 for RSV and 22 for SARS-CoV-2. Among the positive samples for influenza, 57.7% (254 out of 440) were influenza A(H1N1)pdm09, 5.9% (26 out of 440) were influenza A(H3N2), 10.0% (44 out of 440) were influenza A(not subtyped) and 26.4% (116 out of 440) were influenza B. The highest amount of positive influenza samples were in week 51 (week commencing 16 December) 2024 (13.4%; 59 out of 440) and a majority of positive influenza samples (88.9%; 391 out of 440) were received between weeks 48 (week commencing 25 November) 2024 and week 8 (week commencing 17 February) 2025.

Figure 23. Weekly number of samples testing positive for influenza, RSV and SARS-CoV-2, GP sentinel practices, Northern Ireland, 2024 to 2025 season

Wales

Between week 40 (week commencing 30 September) 2024 and week 12 (week commencing 17 March) 2025, influenza cases via GP sentinel swabbing increased from week 47 (week commencing 18 November 2024), predominantly due to influenza A(H1N1)pdm09 activity. Cases peaked in week 51 (week commencing 16 December) 2024 and then gradually declined until stabilising around week 4 (week commencing 20 January). Influenza B cases increased around week 7 (week commencing 10 February) 2025 and persisted until the data cut-off for this report. By the end of the reporting period, 1,675 cases of influenza were detected.

Among the other viruses tested, the most detections were rhinovirus (1,244 samples positive), RSV (633 samples positive) and hMPV (567 samples positive). Please note that figure 24 groups pathogens detected less frequently together. See the datafile for full details of results.

Figure 24. Weekly test counts for all tested pathogens through GP sentinel practices, Wales, 2024 to 2025 season

Secondary care surveillance

Influenza hospital admissions

England

Surveillance of influenza admissions to Intensive Care Units (ICU) and High-Dependence Units (HDU) is based on mandatory reporting by NHS acute trusts in England. Surveillance of influenza hospitalisations to all levels of care (inclusive of ICU or HDU) is based on data from a small sentinel network of acute NHS trusts in England. Trusts submit weekly aggregate data on new influenza admissions and these are summed and converted to rates per 100,000 by linking to catchment populations of participating trusts in that week. Please see Sources of surveillance data for influenza, COVID-19 and other respiratory viruses for additional details on data collection and calculation of admission rates. All 2024 to 2025 season data presented in this report were collected between week 40 2024 and week 14 2025 inclusive, with previous season comparisons including week 40 2023 to week 14 2024 inclusive.

Influenza hospital admissions (SARI-Watch sentinel surveillance)

As a sentinel surveillance system, the number of trusts volunteering to participate may vary between seasons. Therefore, rates of hospitalised influenza cases are presented here to compare between different seasons.

Overall activity

A total of 16,391 test confirmed influenza hospital admissions were reported by 29 participating trusts in the 27 week period. Of 29 trusts, 26 were regular reporters participating in 19 weeks or more.

Cumulative rates presented are based on a sum of weekly rates which take into account only trusts participating in that week. The cumulative admission rate was 139.5 per 100,000 trust catchment population. This was higher than a cumulative admission rate of 77.5 per 100,000 in the 2023 to 2024 season and higher than a cumulative admission rate of 94.2 per 100,000 in the 2022 to 2023 season.

Summary of epidemic activity

The overall influenza hospital admission rate breached the baseline MEM threshold in week 47 2024. By comparison, in the 2023 to 2024 season the rate breached the baseline threshold in week 49 2023.

The overall rate peaked at 16.18 per 100,000 in week 52 2024 within the high impact range. This peak was higher than the peak in the 2023 to 2024 season (7.55 per 100,000). By week 14 2025, the epidemic returned to baseline levels marking a period of 19 weeks above baseline impact activity (Figure 25). This compares with 16 weeks above baseline impact activity in the 2023 and 2024 season. Further comparisons to previous seasons are presented in Figure 25.

Admission rates were highest in those aged 85 and above, peaking at 99.85 per 100,000 in week 52 2024 (Figure 26).

Figure 25. Weekly influenza hospital admission rates per 100,000 trust catchment population with MEM thresholds, reported through SARI Watch sentinel surveillance, England

Figure 26. Weekly hospital admission rate by age group for new influenza cases, reported through SARI Watch sentinel surveillance, England [note 6]

Note 6: the highlighted line corresponds to the age group in the subplot title, grey lines correspond to all other age groups.

Influenza hospital admissions by type and subtype

Of the 16,391 influenza hospital admissions reported, 13,752 (83.9%) were influenza A and 2,639 (16.1%) were influenza B.

Influenza A hospital admissions peaked in week 52 2024. A large proportion 88.2% (12,134 out of 13,752) of influenza A cases were reported as influenza A unknown. For comparison, the proportion of influenza A unknown cases was lower in the 2023 to 2024 season at 76.9% (5,780 out of 7,518).

Among influenza A admissions with subtyping information, there were 1,480 (91.5%) influenza A(H1N1)pdm09 and 138 (8.5%) influenza A(H3N2) cases.

There was an increase in influenza B cases from January 2025, peaking in week 8 2025 (week commencing 17 February). Influenza type and subtype proportions by age-group are presented in Figure 27.

Figure 27. Proportion of influenza hospital admissions by influenza type and age group, reported through SARI Watch sentinel surveillance, England (week 40 2024 to week 14 2025)

Scotland

Influenza admissions are captured from Rapid Preliminary Inpatient Data (RAPID), which consists of daily submissions of inpatient hospital admissions in Scotland. Influenza admissions are defined as patients with an emergency admission (excluding surgical, mental health specialties, or emergency admissions with diagnostic codes related to injuries), who have a positive influenza test results within 14 days before and 2 days after admission.

In the 2024 to 2025 season, admission rates started to increase in week 48 2024 (week commencing 25 November) and peaked in week 52 2024 (week commencing 23 December) at 1,600 admissions (29 per 100,000 population) and declined thereafter. Cumulative rates were higher than in the 2023 to 2024 and 2022 to 2023 seasons.

Peak activity was attributable to influenza A. In samples which had full sequencing results, the majority were influenza A(H1N1)pdm09. There were a limited number of influenza B admissions later in the season, with the peak influenza B admission count (92 admissions) occurring in week 10 (week commencing 3 March) 2025.

Figure 28. Weekly influenza hospitalisation rates through RAPID by season, Scotland, 2022 to 2025

Figure 29. Weekly influenza hospitalisation counts by influenza subtype, Scotland, 2024 to 2025 season

Northern Ireland

Community-acquired influenza admissions to hospitals are estimated by combining data from the Patient Administration System (PAS) and influenza test results from the Northern Ireland Health Analytics Platform (NIHAP). Cases are defined by a combination of an emergency admission associated with a positive influenza test between seven days before and one day after admission. All trusts in Northern Ireland contribute to this data collection.

Influenza admission activity increased from week 47 2024 (week commencing 18 November) showing a single peak in week 51 2024 (week commencing 16 December) at 21.3 per 100,000 population before steadily declining to low levels, reaching 1.8 per 100,000 population in week 14 2025 (week commencing 31 March). There was a total of 2,808 emergency admissions, with a cumulative admission rate of 146 per 100,000 population. Overall, 754 emergency admissions were influenza A(H1), 98 were influenza A(H3), 1,566 were influenza A(not subtyped) and 390 were influenza B. The majority of influenza A emergency admissions was reported in those aged 75 years and older (33.7%; 814 out of 2,418). The number of influenza B emergency admissions surpassed influenza A emergency admissions from week 6 2025 (week commencing 3 February) with adolescents and young adults (those aged 15 to 44 years of age) being the age group most represented in influenza B admissions (40.5%; 158 out of 390).

Figure 30. Weekly influenza hospital admission rate by season, Northern Ireland, 2022 to 2025

Figure 31. Weekly number of influenza admissions by subtype, Northern Ireland, 2024 to 2025 season

Wales

Hospitalised influenza cases in Wales are identified by linking hospital admissions recorded in the Wales Patient Administration Systems (PAS) to laboratory test results using patient NHS number. Cases are defined as those admitted to hospital who tested positive for influenza within 28 days prior to admission or up to day 2 of an inpatient stay (where admission date is day 1).

A total of 2,388 hospitalised influenza cases were reported in Wales from week 40 (week commencing 30 September) 2024 to week 12 (week commencing 17 March) 2025. Hospital admissions started to increase in week 46 2024 (week commencing 11 November), peaked in week 52 2024 (week commencing 23 December) at 306 admissions and thereafter initially decreased sharply, followed by a more gradual decline.

Figure 32. Weekly influenza hospital admission counts, Wales, 2023 to 2025

Influenza ICU or HDU admissions

England

Influenza ICU-HDU admissions (SARI-Watch mandatory surveillance)

Overall activity

A total of 1,984 test confirmed influenza critical care (ICU or HDU) admissions were reported by 116 trusts in England. This compares with 874 critical care influenza admissions reported by 112 trusts from week 40 2023 to week 14 in 2024.

Cumulative rates presented are based on a sum of weekly rates which takes into account only trusts participating in that week. The cumulative rate was 4.11 per 100,000 trust catchment population based on data from week 40 2024 to week 14 2025. In the 2023 to 2024 season the cumulative rate for the same reporting interval was 1.92 per 100,000 and 3.78 per 100,000 in the 2022 to 2023 season.

Figure 33. Weekly overall influenza ICU or HDU admission rates per 100,000 trust catchment population with MEM thresholds by season, reported through SARI Watch mandatory surveillance, England

Summary of epidemic activity

The ICU or HDU influenza admission rate crossed the baseline threshold in week 49. In the 2023 to 2024 season the admission rate for influenza crossed the baseline threshold in week 51.

The overall rate peaked at 0.54 per 100,000 in week 1 (week commencing 30 December), within the medium impact range. This peak was higher than the peak in the 2023 to 2024 season (0.2 per 100,000). By week 8 (week commencing 17 February), the epidemic returned to baseline levels marking a period of 11 weeks of above baseline impact activity (Figure 33). This compares with 7 weeks of above baseline activity in the 2023 to 2024 season. Further comparisons to previous seasons are presented in Figure 33.

The highest number of cases were among those aged between 15 and 44 years (475 cases). Admission rates were highest in those aged between 75 and 84 years, peaking at 1.36 per 100,000 in week 1. In the 2023 to 2024 season the highest number of cases were among those aged between 15 and 44 years (175 cases) and admission rates were highest in those aged under 5 years, peaking at 0.54 per 100,000 in week 6.

Figure 34. Weekly ICU or HDU admission rate by age group for new influenza cases, reported through SARI Watch mandatory surveillance, England, 2024 to 2025 season [note 6]

Note 6: the highlighted line corresponds to the age group in the subplot title, grey lines correspond to all other age groups.

Influenza ICU or HDU admissions by type and subtype

There were 1,984 influenza cases in ICU or HDU admissions reported. Of these, there were 1,751 (88.3%) influenza A and 233 (11.7%) influenza B cases.

Influenza A ICU or HDU cases peaked in week 1. A large proportion, 82.9% (1,451 out of 1,751), were reported as influenza A unknown. For comparison, the proportion of influenza A unknown cases was 81.6% (677 out of 830) in the 2023 to 2024 season.

Among influenza A admissions with subtyping information, there were 267 (89.0%) influenza A(H1N1)pdm09 and 33 (11.0%) influenza A(H3N2) cases.

There was an increase in influenza B cases later in the season, peaking in week 9 (week commencing 24 February). Figure 35 shows the distribution of influenza ICU or HDU cases by age group, influenza type and subtype in the 2024 to 2025 season.

Figure 35. Weekly influenza ICU or HDU admissions by influenza type, reported through SARI Watch mandatory surveillance, England, 2024 to 2025 season

Scotland

Patients admitted to ICU or HDU with recently confirmed influenza are identified from the Scottish Intensive Care Society Audit Group (SICSAG) that collects detailed patient level data on all patients in ICU/HDU across Scotland. All patients that are admitted to ICU/HDU with a positive influenza test result within a period of 14 days before the ICU or HDU admission and the ICU or HDU discharge date are included. Where the discharge date is missing, any patient with a positive influenza test result within a period of 14 days before ICU/HDU admission and seven days after ICU or HDU admission are included.

Influenza ICU admissions began in November 2024 and peaked in week 52 (week beginning 23 December) 2024 at 77 admissions and declined thereafter. From week 27 (week commencing 1 July) 2024 until week 14 (week commencing 31 March) 2025, a total of 440 ICU admissions were reported. 315 were influenza A without a known subtype, 83 were influenza A(H1N1)pdm09, 12 were influenza A(H3N2) and 30 were influenza B.

Total admissions were higher than in the 2023 to 2024 (282 admissions) and 2022 to 2023 season (355 admissions), which include week 27 until week 26 of the next year.

Figure 36. Weekly influenza ICU admission counts through SICSAG by subtype, Scotland, 2024 to 2025 season

Wales

Data from Wales are for patients swabbed and testing positive for influenza whilst in ICU settings, as indicated by the test location code in the all-Wales laboratory test database (Datastore). The number of individuals with influenza admitted to ICU is likely to be higher as some individuals may not have been tested, or may have been tested outside of ICU before or after being transferred.

Between week 40 (week commencing 30 September) 2024 and week 12 (week commencing 12 March) 2025, 97 influenza ICU admissions were reported in Wales. Among 42 admissions where subtyping information was available, 34 were positive for influenza A(H1N1)pdm09, 2 were positive for influenza A(H3N2), and 6 were positive for influenza B.

Figure 37. ICU admissions reported by influenza subtype, Wales

ECMO admissions in the UK

UKHSA collects data on adult patients admitted to severe respiratory failure (SRF) centres for extra corporeal membrane oxygenation (ECMO) or other advanced respiratory support. There are 7 SRF centres in the UK (6 in England and 1 in Scotland) participating in the UKHSA ECMO surveillance module. Surveillance is all year round. Please see Sources of surveillance data for influenza, COVID-19 and other respiratory viruses for details on data collection. Please note due to retrospective updates by reporters, the data in this report includes additions from one SRF since the last annual report.

Between week 40 2024 and week 14 2025, there were 172 admissions to SRF centres requiring ECMO in the UK (Figure 1). Of these, test confirmed Acute Respiratory Infections (ARI) accounted for 52.9% (91), suspected ARI (where causative pathogen remained undetermined) accounted for 5.8% (10), non-infection causes accounted for 35.5% (61) and sepsis of non-respiratory origin accounted for 5.8% (10).

Of 91 test confirmed ARI ECMO admissions in the 2024 to 2025 season (week 40 2024 to week 14 2025), 63.7% (58) were for influenza (23 influenza A (not subtyped), 9 influenza A(H3N2), 16 influenza A(H1N1)pdm09 and 10 influenza B cases). In this period, there was 1 COVID-19 admission and 2 RSV admissions.

In the previous season (week 40 2023 to week 14 2024), there were 121 admissions to SRF centres requiring ECMO in the UK. Of these, test confirmed ARI accounted for 39.7% (48), suspected ARI accounted for 8.3% (10), non-infection causes accounted for 45.5% (55) and sepsis of non-respiratory origin accounted for 6.6% (8).

Of 48 test confirmed ARI cases, there were 20 admissions for influenza (9 influenza A (not subtyped), 4 influenza A(H3N2), 7 influenza A(H1N1)pdm09 and 0 influenza B cases). This compares with 46 influenza admissions in the 2022 to 2023 season (week 40 2022 to week 14 2023). For COVID-19, there were 2 admissions in 2023 to 2024 and 3 in 2022 to 2023. For RSV, there were 0 admissions in 2023 to 2024 and 2 in 2022 to 2023.

Figure 38. Weekly all cause ECMO admissions in adults to severe failure centres in the UK, inclusive of admissions for test confirmed influenza, COVID-19 and RSV Acute Respiratory Infections (ARI).

Laboratory surveillance

Second Generation Surveillance System (SGSS), England

The Second Generation Surveillance System (SGSS) captures test result information for notifiable infectious diseases, including influenza, from laboratories in England. In this section, positivity rate, or the percentage testing positive, is presented as a 7-day rolling average, with the number of individuals testing positive for influenza during the preceding 7 days divided by the number of individuals tested overall during the preceding 7 days through PCR testing. Test records are deduplicated using patient identifiers, such that each record indicates how many tests are attributed to an individual each day and how many of these tests were positive. Further details can be found in our data quality report.

In the 2024 to 2025 season influenza positivity rates gradually increased from mid-September, with the rate of increase accelerating mid-November: the 7-day moving average positivity rate estimate doubled between 15 November (4.1%) and 25 November (9.2%). Positivity rate estimates peaked at 31% at the end of December 2024. The overall positivity rate declined thereafter, but at a notably slower rate that in the 2022 to 2023 season. Considering the whole season, testing positivity was higher than in the 2023 to 2024 and 2022 to 2023 seasons.

By age, similar increases were visible in most age groups, where school-aged children appeared to have the earliest increase and subsequently the highest positivity rate throughout the season. However, patterns of decline varied across age groups. In adults aged 55 years and above, the positivity rate declined steadily after the peak in the end of December. Conversely, in school-aged children and younger adults (up to 44 years of age) the positivity rate decline appeared to stabilise mid-January until mid-March and thereafter slowly declined.

Figure 39. Daily percentage of tests positive for influenza among all reported influenza tests (7-day rolling average), England [note 7]

Note 7: data from previous seasons is aligned by day.

Figure 40. Daily percentage of tests positive for influenza among all reported influenza tests by age group (7-day rolling average), England [note 6]

Note 6: the highlighted line corresponds to the age group in the subplot title, grey lines correspond to all other age groups.

Respiratory Datamart, England

Influenza

The Respiratory Datamart system began during the 2009 influenza pandemic to collate all laboratory testing information in England. It is now used as a sentinel laboratory surveillance tool, monitoring all major respiratory viruses in England. 14 laboratories in England, including 5 public health laboratories, 8 NHS hospital laboratories and a UKHSA national laboratory, reported data for this season. The majority of samples were received from hospitals.

Overall influenza positivity was above 5% between week 48 of 2024 (week commencing 25 November) and week 11 of 2025 (week commencing 10 March). Peak positivity (27.8%) above that seen in the 2023 to 2024 season (17.6%) and comparable to the 25.3% peak in 2019 to 2020 and 28.6% peak in 2018 to 2019 season (44), noting that these seasons were before the circulation of SARS-CoV-2 and introduction of COVID-19 testing.

The majority of detections were influenza A. Of the detected influenza A viruses that were subtyped, the majority were influenza A (H1N1)pdm09. Influenza B positivity increased to levels between 1.8% and 5.2% between week 3 (week commencing 13 January 2025) and 14 (week commencing 24 March 2025). Influenza B activity was more limited in older adults.

Figure 41. Weekly percentage of tests positive for influenza, Respiratory Datamart sentinel laboratories, England, by season

Figure 42. Weekly percentage of tests positive for influenza by age and influenza type, Respiratory Datamart sentinel laboratories, England, 2024 to 2025 season

Figure 43. Number of positive tests by influenza subtype, Respiratory Datamart sentinel laboratories, England, 2024 to 2025 season

Figure 44. Weekly number of influenza detections by subtype and overall percentage positivity, Respiratory Datamart, England, 2017 to 2025

Other seasonal respiratory viruses

Of the other respiratory viruses monitored through the Respiratory DataMart system, the highest levels of positivity were observed with rhinovirus throughout the season. Positivity for rhinovirus peaked in week 40 2024 (week commencing 30 September) at 17%. Parainfluenza activity remained low throughout the season but activity commonly increases around the period coinciding with publication of this report. Human metapneumovirus (hMPV) levels were similar compared to previous season, with recent activity pointing towards a spring peak. Adenovirus positivity estimates were low throughout the season and similar to previous seasons.

Figure 45. Weekly percentage of samples testing positive for rhinovirus, adenovirus, parainfluenza and hMPV, DataMart sentinel laboratories, England, by season

Scotland

All NHS laboratories in Scotland submit data for positive influenza tests via the Electronic Communication of Surveillance Scotland (ECOSS) database. Estimates presented here are after removal of tests that are done through sentinel testing (such as CARI). As of the 2023 to 2024 season, data submitted by all NHS laboratories include negative results for influenza. Between the 2010 to 2011 and 2022 to 2023 seasons, there was a staggered rollout of laboratories submitting negative results for influenza tests. Positivity estimates are calculated as proportion positive tests divided by all tests in a given week. Case counts are calculated after deduplication of positive tests within the same patient.

In the 2024 to 2025 season, positivity increased from week 47 (week commencing 18 November) and peaked in week 52 (week commencing 23 December) at 35.5% an declined thereafter. Across the majority of weeks, positivity was higher than in the 2023 to 2024 and 2022 to 2023 seasons (Figure 46).

The first half of the 2024 to 2025 season was driven by influenza A. Of subtyped samples, most samples were influenza A(H1N1)pdm09. In the second half of the season, there was a gradual increase in influenza B detections (Figure 47).

Figure 46. Weekly percentages of tests positive for influenza through ECOSS, Scotland, by season

Figure 47. Weekly tests positive for influenza by influenza subtype reported through ECOSS, Scotland, 2024 to 2025 season

Northern Ireland

Results of all positive and negative influenza testing from the Regional Virus Laboratory (RVL) and all local laboratories are collated into The Northern Ireland Health Analytics platform (NIHAP). Microbiological surveillance is the monitoring of influenza from virology data collected from settings such as hospitals and GP surgeries. The majority of samples were received from hospitals.

Overall influenza positivity showed an increased level of activity (above 5%) from week 46 (commencing 11 November 2024) and remained just above this threshold in week 14 2025 (commencing 31 March 2025) at 5.1%. Peak positivity was seen in week 52 2024 (week commencing 23 December 2024) at (35.2%) which was higher than that seen in the 2023 to 2024 (21.8%).

The majority of detections were influenza A (Figure 49). Of the detected influenza A viruses that were subtyped, the majority were influenza A(H1N1)pdm09 (87.9%). Influenza B detections started increasing from week 49 2024 (week commencing 2 December), surpassing influenza A from week 6 2025 (week commencing 3 February). Peak positivity for influenza B was seen in week 9 2025 (week commencing 24 February) at 6.5%.

Figure 48. Weekly percentage tests positive for influenza by season from NIHAP, Northern Ireland, by season

Figure 49. Weekly positive influenza tests by influenza subtype from NIHAP, Northern Ireland, 2024 to 2025 season

Wales

Diagnostic virology results from Wales concern all test results in Wales present in the Datastore. These are from patients tested from non-sentinel settings. The vast majority of these patients are in hospital, with a small proportion from non-sentinel community sources.

Out of 29,691 samples tested between week 40 (commencing 30 September) 2024 and week 12 (week commencing 18 March) 2025, 3,151 tested positive for influenza A, and 379 tested positive for influenza B. Overall influenza positivity started to increase in week 47 2024 (week commencing 18 November) and peaked in week 52 2024 (week commencing 23 December) at 29.7% and declined thereafter. At the data cut-off for this report, positivity was 7%.

Figure 50. Weekly percentage of tests positive for influenza through Datastore, Wales, by season

Virus characterisation

England

UKHSA characterises the properties of influenza viruses through one or more tests, including genome sequencing (genetic analysis) and haemagglutination inhibition (HI) assays (antigenic analysis). This data is used to compare how similar the circulating influenza viruses are to the strains included in the vaccines, and to monitor for changes in circulating influenza viruses. Antigenic similarity of circulating influenza strains to vaccine strains is defined as having an antibody titre within a 4-fold range when compared to reference viruses representative of the vaccine strain.

Between week 40 2024 and week 16 2025, the UKHSA Respiratory Virus Unit have genetically characterised, by sequencing of the haemagglutinin (HA) gene, 1461 influenza A viruses (338 A(H3N2) and 1,123 A(H1N1)pdm09 viruses) and 791 influenza B viruses.

The 1,123 characterised influenza A(H1N1)pdm09 viruses all belong in genetic clade 5a.2. The Northern Hemisphere 2024-2025 influenza A(H1N1)pdm09 vaccine strain (an A/Victoria/4897/2022-like virus) also belongs in this genetic clade. 92.4% of viruses belonged to clade 5a.2a, subclade C.1.9 and 7.6% belong to clade 5a.2a.1 major subclade D (which has been further split into 5 subclades, D.1-D.5). Subclades with their defining amino acid substitutions are presented in table 2. The proportion of 5a.2a.1 detections increased later in the season (Figure 51).

183 A(H1N1)pdm09 viruses have been antigenically characterised and 183 (100%) were similar to reference viruses representative of the A/Victoria/4897/2022 (H1N1)pdm09‑like Northern Hemisphere 2024-2025 A(H1N1)pdm09 vaccine strain.

Table 2. Number of influenza A(H1N1)pmd09 viruses characterised by genetic and antigenic analysis at the UKHSA Respiratory Virus Unit, England, 2024 to 2025 season

Clade	Subclade	Defining amino acid substitutions	Number of detections	Percentage
5a.2a	C.1.9	5a.2a plus K169Q	1,038	92.4%
5a.2a.1	D	5a.2a.1 plus T216A	1	0.1%
5a.2a.1	D.1	D plus R45K(nt 1688A) and L3219I	4	0.4%
5a.2a.1	D.3	D plus T120A and I372V	73	6.5%
5a.2a.1	D.5	D plus R45K (nt 1688)T	7	0.6%

Figure 51. Monthly proportion of influenza A(H1N1)pdm09 subclades genetically characterised through RVU, England, 2024 to 2025 season

The 338 influenza A(H3N2) viruses detected during the 2024 to 2025 season all belong in the genetic clade 2. The Northern Hemisphere 2024-2025 influenza A(H3N2) vaccine strain (an A/Thailand/8/2022-like virus) also belongs in this genetic clade. Haemagglutinin (HA) gene sequence shows that 99.4% of the influenza A(H3N2) viruses belong in clade 2a.3a.1 subclade J distributed between several lineages, with the majority in J.2 (Table 3). Detections of the J.2.2 subclade with, additional amino acid substitutions, increased towards the end of the season (Figure 52).

Table 3. Number of influenza A(H3N2) viruses characterised by genetic and antigenic analysis at the UKHSA Respiratory Virus Unit, England, 2024 to 2025 season

Clade	Subclade	Defining amino acid substitutions	Number of detections	Percentage
2a.3a	G.1.3.1	2a.3 plus E50K	2	0.6%
2a.3a.1	J	2a.3 plus E50K, I140K and I223V	1	0.3%
2a.3a.1	J.1.1	J.1 plus S145N	10	2.9%
2a.3a.1	J.2	J plus N122D(-CHO) and K276E	263	77.8%
2a.3a.1	J.2.1	J.2 plus P239S	9	2.7%
2a.3a.1	J.2.2	J.2 plus S124N	53	15.7%

Figure 52. Monthly proportion of influenza A(H3N2) subclades genetically characterised through RVU, England, 2024 to 2025 season.

73 A(H3N2) viruses have been antigenically characterised and 60 (82%) were similar to reference viruses representative of the A/Thailand/8/2022 (H3N2)‑like Northern Hemisphere 2024-2025 (H3N2) vaccine strain.

The 791 influenza B/Victoria lineage viruses all belong in clade V1A.3a.2. The Northern Hemisphere 2024 to 2025 influenza B/Victoria lineage vaccine strain (a B/Austria/1359417/2021-like virus) also belongs in this clade. The clade and subclade distribution of influenza B viruses detected in the 2024 to 2025 respiratory virus season are shown in Table 4. Subclade C.5.1 was the most frequently detected with the proportion in this subclade increasing over the course of the season (Figure 53).

Table 4. Number of influenza A(H1N1)pmd09 viruses characterised by genetic and antigenic analysis at the UKHSA Respiratory Virus Unit, England, 2024 to 2025 season

Clade	Subclade	Defining amino acid substitutions	Number of detections	Percentage
V1A.3a.2	C.3	C plus E128K, A154E and S208P	2	0.3%
V1A.3a.2	C.5	C plus D197E	15	1.9%
V1A.3a.2	C.5.1	C.5 plus E183K	334	42.2%
V1A.3a.2	C.5.6	C.5 plus D129N	283	35.8%
V1A.3a.2	C.5.7	C.5 plus E128G and E183K	157	19.8%

Figure 53. Monthly proportion of influenza B subclades genetically characterised through RVU, England, 2024 to 2025 season.

72 influenza B viruses have been antigenically characterised and 72 (100%) were similar to reference viruses representative of the B/Austria/1359417/2021 (B/Victoria lineage)‑like Northern Hemisphere 2024 to 2025 influenza B vaccine strain.

Genome sequencing has confirmed the detection of LAIV viruses in 3 influenza A positive samples and 5 influenza B positive samples collected since week 40 2024, all from children aged between 2 and 16 years of age, who have presented with mild respiratory illness shortly after receiving LAIV, consistent with known shedding characteristics of LAIV viruses.

Scotland

Virus characterisation in Scotland is performed by the West of Scotland Specialist Virology Centre (WoSSVC) throughout the influenza season on a small number of influenza samples. Between week 40 (week commencing 30 September) 2024 and week 12 (week ending 23 March) 2025, the 101 influenza A(H1N1)pdm09 viruses characterised all belong in genetic clades 5a.2a and 5a.2a.1. The Northern hemisphere 2024 to 2025 season influenza A(H1N1)pdm09 vaccine strain (an A/Victoria/2570/2019-like virus) generally recognised both these clade viruses well.

Of the 20 influenza A(H3N2) viruses genetically characterised, almost all belonged to subclade 2a.3a.1 (J.2), with one belonging to 2a.3a (G.1.3.1). The Northern hemisphere 2024 to 2025 season influenza A(H3N2) vaccine strain (an A/Thailand/08/2022-like virus) showed reduced reactivity to the majority of viruses tested globally.

There were 33 influenza B/Victoria lineage viruses genetically characterised, all belonging in clade V1A.3a.2. The Northern hemisphere 2024 to 2025 season influenza B/Victoria lineage vaccine strain (a B/Austria/1359417/2021-like virus) also belongs in this clade.

Influenza antiviral susceptibility, England

Molecular surveillance by whole-genome sequencing (WGS) is used to monitor the susceptibility of circulating influenza A and B viruses by comparing sequence data of the neuraminidase and polymerase genes against the World Health Organisation (WHO) reference tables summarising the amino acid substitutions in the respective influenza genes associated with resistance or reduced susceptibility to neuraminidase (NA) inhibitors or baloxavir marboxil, respectively.

Sequence data from surveillance samples collected in primary and secondary care (with no known antiviral exposure) are routinely evaluated for presence of amino acid changes associated with reduced inhibition by antiviral drugs. If amino acid substitutions associated with resistance or reduced susceptibility to antivirals are identified, the details of potential drug exposure are investigated. Additionally, a small number of samples may also be received with specific requests for antiviral resistance testing (for example from patients after treatment).

Influenza virus sequences from samples collected between weeks 40 (week commencing 30 September) 2024 and week 16 (week commencing 14 April) 2025 have been analysed. Within the 323 influenza A(H3N2) viruses, no markers associated with reduced inhibition were identified. Of the 1,102 A(H1N1)pdm09 and 782 influenza B virus NA sequences, 22 oseltamivir and/or zanamivir resistant viruses were found, which were collected from 20 patients, 12 of which had evidence of drug treatment as shown in table 5 below.

Table 5. Details on mutations detected and patient characteristics for samples with genotypic markers of antiviral resistance.

Subtype	Mutation detected	Number of patients detected with the mutation	Immunocompromised (Oseltamivir received)	Immunocompromised (Oseltamivir not received)	Immunocompetent (Oseltamivir received)	Immunocompetent (Oseltamivir not received)	Unknown [note 8]
H1N1pdm09	H275Y	16	10	2	1	0	3
H1N1pdm09	I427T	1	0	0	0	1	0
H1N1pdm09	I223M	1	0	0	0	1	0
B	T146K	1	0	0	0	1	0
B	G407S	1	0	0	0	1	0
B	G145R	1	0	0	1	0	0
B	N294S	1	0	0	0	1	0
Total	Total	22	10	2	2	5	3

Note 8: patient immune status and exposure to antiviral drugs unknown at the time of publication of this report.

There were 16 influenza A(H1)pdm09 viruses identified with the H275Y amino acid substitution which is linked to resistance to oseltamivir. Two influenza A(H1N1)pdm09 viruses with an amino acid change (I427T and I223M, respectively) previously characterised as associated with reduced inhibition by oseltamivir and zanamivir (I427T only) were detected. There were no known markers of reduced inhibition by NA inhibitors detected in a further 1,084 influenza A(H1)pdm09 NA sequences analysed.

4 influenza B viruses with an amino acid change (G145R, T146K, N294S and G407S, respectively) previously characterised as associated with reduced inhibition by NA inhibitors were detected. There were no known markers of reduced inhibition by NA inhibitors detected in further 778 influenza B NA sequences analysed.

No viruses with known markers of resistance to baloxavir marboxil were detected in 316 A(H3N2), 794 A(H1N1)pdm09 and 766 influenza B PA sequences analysed.

Age Stratified Population based serology

A pre-season seroprevalence study was undertaken, to assess population susceptiblility to seasonal influenza viruses. We analysed a convenience sample of residual age-stratified sera, geographically representative of England collected during the period January to July 2024 through the RCGP-RSC (Royal College General Practitioners Research and Surveillance Centre) serology collection from patients aged over 18 years. Paediatric sera were sourced from the UKHSA Sero-epidemiology Unit (SEU) serology collections.

We measured presence of antibody to influenza A components of cell based 2024/25 seasonal influenza vaccines, A/Wisconsin/67/2022 ((H1N1)pdm09-like virus; clade 6B.1A.5a.2a.1) and A/Massachusetts/18/2022 ((H3N2)-like virus; clade 3C.2a1b.2a.2a.3a.1) in these materials by haemagglutination inhibition (HI) antibody.

Overall, seroprevalence was higher for A(H3N2) than A(H1N1)pdm09. The evaluation of HI data by age took place for ten age groups:

• 1 to 5 years of age
• 6 to 10 years of age
• 11 to 15 years of age
• 16 to 24 years of age
• 25 to 34 years of age
• 35 to 47 years of age
• 48 to 56 years of age
• 57 to 67 years of age
• 68 to 78 years of age
• 79 years of age and above

The evaluation showed antibody levels in children increased with age up to children aged between 11 and 15 years of age and a low percentage of individuals with seroprotective titres (HI titre above or equal to 40) against influenza A(H3N2) in those aged 48 to 56 years, where seroprotection rates were 40.1% (95% confidence interval (CI) 31.1 to 49.5%) and the GMT was 18.6 (95% CI 14.5 to 23.9).

For influenza A(H1N1)pdm09, seropositivity and geometric mean titres (GMT) were lowest in those aged 35 to 47 and in the oldest age group (79 years of age and above) with seroprotection rates of 23.7% (95% CI 15.2 to 33.3%) and 28.2% (19.9 to 37.8%), respectively with GMT of 12.3 (95% CI 9.1 to 16.6) and 13.8 (95% CI 11 to 17.4), respectively.

Titres against A(H1N1)pdm09 and A(H3N2) are higher in those with a record of recent vaccination in the 2023 to 2024 season). Low antibody titres were seen in the very young (2 years of age or younger), this age group is not eligible for the live, attenuated influenza vaccine (LAIV).

The noticeable lack of antibody in the mid age bracket (35 to 47 years of age) and low portion with antibody titres above the protective threshold of HI 40 and above, especially with A(H1N1)pdm09 indicates the susceptibility of this age group.

Mortality

Influenza-attributable deaths

The FluMOMO model has been used by the UK Health Security Agency (UKHSA) for many years to estimate influenza-related mortality, adjusting for extreme temperature, and is published in annual reports. However, with the COVID-19 pandemic leading to very large mortality levels from late March 2020, and with very little influenza circulation in 2020 to 2021 and 2021 to 2022 winters, models were not run in those years. For the 2022 to 2023 season, a new model was developed to incorporate COVID-19, details of which are given in the 2023 working paper.

In the 2024 to 2025 season the FluMOMO model was run using data from 1 October 2012 to 30 March 2025. Further details of the model for this season, with comparisons to the 2024 model are given in the 2025 working paper. Briefly, the model estimates attributable mortality based on the pattern of all cause deaths by week compared to that seen for influenza activity, extreme cold or heat and COVID-19 death certifications. It allows an estimate of attributable mortality irrespective of whether deaths are recorded as due to these factors.

During the 2024 to 2025 season, influenza circulated above baseline levels from December 2024 to early March 2025. COVID-19 also circulated at low levels throughout the period. There were periods of extreme cold with alerts issued. In the week commencing January 6 2025, the mean weekly temperature was 0.1°C which counted as an extreme low temperature week as it was below the 3°C threshold used in the FluMOMO model.

Figure 54 represents the weekly number of all-age deaths and attribution to influenza, COVID-19 and extreme temperature covering the most recent 3 winters (week 40 2022 to 13 2025). The model demonstrates that in the winter of the 2024 to 2025 season excess mortality was higher than the previous season, with the greatest contributors on top of the baseline (grey) being influenza (red), followed by COVID-19 (blue), and cold weather (green) (Figure 54, Table 6 and Table 7).

Influenza-related mortality for winter the 2024 to 2025 season is estimated at about 7,800 which is much higher than the roughly 3,600 seen in the 2023 to 2024 season, but lower than the estimated 15,900 seen in the 2022 to 2023 season. Compared with pre-pandemic years in the model, the 2024 to 2025 season influenza-attributable mortality was generally lower.

For temperature-related mortality, the 1,400 estimate from the one cold week was similar to the 2023 to 2024 total, but lower than the 2022 to 2023 season which had more colder weeks than the 2024 to 2025 season.

Figure 54. Weekly number of all-age deaths and attribution to influenza, COVID-19 and cold weather, England, week 40 2022 to week 13 2025

Table 6. Estimated number of deaths associated with influenza, by age observed through the adapted FluMOMO algorithm with 95% confidence intervals [note 10], England, 2024 to 2025 season (week 40 2024 to week 13, 2025) [note 9]

Age	Total estimate	Lower 95% CI	Upper 95% CI
0 to 4 years	8	3	15
5 to 14 years	11	6	16
15 to 64 years	1,204	1,136	1,273
65 years and over	6,534	6,150	6,926
Total	7,757	7,363	8,151

Note 9: Estimates in children should be treated with caution, as the method is not calibrated to estimate such small excesses.

Note 10: Confidence intervals do not include uncertainty from model specification.

Table 7. Estimated number of all age deaths associated with influenza, COVID-19 and cold weather observed through the adapted FluMOMO algorithm, England, 2012 to 2013 season to 2024 to 2025 [note 12] [note 13]

Year	Influenza	COVID-19	Cold	Unexplained [note 11]	Total
2012 to 2013	16,870	0	4,405	1,731	23,007
2013 to 2014	1,229	0	0	-5,134	-3,906
2014 to 2015	35,949	0	1,103	-5,744	31,306
2015 to 2016	12,792	0	38	1,579	14,408
2016 to 2017	19,191	0	392	3,591	23,173
2017 to 2018	25,161	0	2,450	7,627	35,239
2018 to 2019	5,537	0	1,069	-3,254	3,352
2019 to 2020	8,973	[x]	0	54,758	63,733
2020 to 2021	0	[x]	3,497	45,986	49,483
2021 to 2022	788	30,583	0	-4,509	26,862
2022 to 2023	15,867	14,198	4,292	6,193	40,549
2023 to 2024	3,555	6,272	1,484	212	11,523
2024 to 2025	7,757	2,763	1,439	-889	11,071

[x] Data is not available.

Note 11: Unexplained is negative if the estimated excess from influenza, COVID-19 and cold weather is more than the observed total excess above the baseline.

Note 12: Year is week 40 of one year to week 20 of the next except 2024 to 2025 which ends on week 13.

Note 13: Deaths from week 12 2020 to week 26 2021 were excluded from the modelling, the unexplained excess in 2019 to 2020 and 2020 to 2021 will be almost all due to COVID-19.

Paediatric mortality

Paediatric mortality offers insight into the severity of an influenza season. Children, particularly those under five or with underlying health conditions, are more vulnerable to severe outcomes.

Influenza-related deaths within each season were measured using positive influenza cases from SGSS and ONS all-cause mortality data. Laboratory confirmed influenza case records were linked to the deaths recorded in the NHS spine using demographic batch service tracing as well as ONS all-cause mortality records to indicate where a case had died within 28 days of their earliest positive specimen within that season. ONS all-cause mortality data was also used to identify deaths where influenza was mentioned as a cause of death on an individual’s death certificate.

Between 6 October 2024 and 6 April 2025 (week 40 to week 14), an estimated 53 influenza-related deaths occurred in children under 18 years of age. For comparison, an estimated 35 paediatric influenza-related deaths were reported in the 2023 to 2024 season (1 October 2023 to 18 May 2024), and 72 deaths in the 2022 to 2023 season (2 October 2022 to 20 May 2023).

Please note that there are significant reporting lags in mortality data. At the time of publication, data are available only up to week 14 for the 2024 to 2025 season, whereas for previous seasons, data are available up to week 20. The date range refers to the date of death and includes individuals who tested positive for influenza up to 28 days prior. Influenza-related deaths were identified using ICD-10 codes J09, J10, and J11. All deaths where influenza was mentioned as a cause of death on an individual’s death certificate had a positive laboratory test result for influenza and had died within 28 days of their earliest positive specimen.

Table 8. Estimated number of deaths associated with influenza in those aged under 18 years, England, 2022 to 2025

Cause	2022 to 2023 season	2023 to 2024 season	2024 to 2025 season
Deaths where influenza was mentioned on death certificate	47	12	30
Deaths within 28 days of a positive influenza test	72	35	53
Total influenza related deaths	72	35	53

Vaccination

Seasonal influenza vaccine uptake in adults

Although all nations use standardised specifications to extract vaccine uptake data from IT information systems in primary care (GP system suppliers), there are some differences in extraction specifications, so comparisons between nations should be made with caution.

England

In England, the uptake of seasonal influenza vaccine is monitored by UKHSA throughout the season based on weekly and monthly extracts from GP system suppliers via ImmForm for the cohorts where vaccinations are primarily delivered via the GP practice.

During the 2024 to 2025 season, for the first time adult groups (excluding pregnant women) were eligible from 3 October, rather than 1 September as in previous seasons. Therefore, data for those aged 65 years and over, and those aged under 65 years in clinical risk groups and frontline healthcare workers, is not directly comparable with previous seasons. As in previous seasons, children and pregnant women were eligible from 1 September.

Cumulative uptake of influenza vaccinations administered up to 28 February 2025 was reported from 98.7% (6,148 out of 6,229) of GP practices in England in the 2024 to 2025 season. Comparative data is up to 29 February 2024 where vaccine uptake was reported from 96.9% (6,152 out of 6,346) of GP practices in England in the 2023 to 2024 season.

This season saw a vaccine uptake of 74.9% in those aged 65 years and over (compared with 77.8% in the 2023 to 2024 season) and 40.0% for those aged 6 months to under 65 years of age with one or more underlying clinical risk factors (excluding pregnant women without other risk factors and carers), compared with 41.4% in the 2023 to 2024 season. Vaccine uptake in pregnant women was 35.0%, compared with 32.1% in the 2023 to 2024 season.

In frontline healthcare workers, (combined total for trusts and GP practices) the total uptake was 37.8%. In trusts, vaccine uptake was 37.5% (from 92.3% of trusts responding), a decrease from 42.8% vaccine uptake in the 2023 to 2024 season (from 93.6% of trusts responding). In GP practice, vaccine uptake was 51.5% (from 9.6% of GP practices), a decrease from 61.8% (from 9.9% of GP practices) in the 2023 to 2024 season.

Table 9. Vaccine uptake in target groups in the England, 2024 to 2025 season

Target group	Number vaccinated	Denominator	% Uptake
65 years and over	8,494,489	11,338,042	74.9
6 months to under 65 years and at risk	3,729,463	9,318,550	40.0
Pregnant with no risk factors	189,677	564,036	33.6
Pregnant with risk factors	35,411	78,862	44.9
All pregnant	225,088	642,898	35.0
Frontline Healthcare workers	458,097	1,212,471	37.8

Further detail on final influenza vaccine uptake data in GP patients in England is available on GOV.UK.

Scotland

The uptake of seasonal influenza vaccine is estimated by PHS throughout the season, using a combination of aggregated data returns submitted by staff in all the territorial NHS boards on a weekly basis for those eligible in the following cohorts: 6 months to 2 years of with risk factors, 2 to 5 years not attending school, primary and secondary school pupils, and weekly extracts of data downloaded from the national clinical data store (NCDS) which contains individual-level data for adults eligible for flu vaccine, and for one NHS board, the data relating to the childhood schools’ and nurseries’ programmes. Please note pregnancy uptake data is not available for 2024 to 2025. Update is representative of the current living Scottish population of each respective eligible cohort.

By the end of week 14 2025 (ending 6 April 2025), among adults aged 65 years and older, 74.1% were vaccinated against influenza during the 2024 to 2025 season (compared with 79.8% in the 2023 to 2024 season). Among at risk groups, 34.6% have been vaccinated against influenza (compared with 42.2% in the 2023 to 2024 season). In health and social care workers, the combined uptake was 35.9%, a decrease from 42.2% vaccine uptake in the 2023 to 2024 season.

Northern Ireland

In Northern Ireland, influenza vaccine uptake is determined using data extracted from the regional Immunisation Information System developed by the Department of Health Digital team, known as the Vaccine Management System (VMS). Eligible groups are not mutually exclusive and individuals may be counted in more than one group. Individuals may have more than one eligibility criteria for vaccination, however most will only have one reason for vaccination recorded on VMS. This will impact estimates of vaccine uptake. Vaccine uptake figures may be subject to revision with improvements in data collection and reporting. Further information on methodology including definitions, caveats and data sources can be found in the Northern Ireland seasonal influenza vaccination surveillance report.

Vaccine uptake was 73.6% in adults aged 65 years and over in the 2024 to 2025 season, compared with 78.0% in the 2023 to 2024 season. The offer of seasonal influenza vaccination in Northern Ireland was extended to include all individuals aged 50 to 64 years from January 2025, similar to the extended offer in January 2024. Uptake was 25.9% in those aged 50 to 64 years (compared with 28.9% in 2023 to 2024). In those aged 18 to 49 years with clinical risk factors, vaccine uptake was 23.4%, compared with 11.9% in 2023 to 2024. Recording of eligibility criteria in VMS improved in the 2024 to 2025 season. Data on vaccine uptake in pregnant women is not available for 2024 to 2025 at date of the current report.

Influenza vaccine was offered to all healthcare workers. Uptake in all healthcare workers employed in NHS trusts (thus excluding social care) was 23.6%, compared with 24.4% in 2023 to 2024.

Wales

In Wales, the uptake of seasonal influenza vaccine is monitored on a weekly basis by Public Health Wales throughout the season based on automated weekly extracts of Read coded data using software installed in all General Practices through the Audit+ Data Quality System. Cumulative uptake data on influenza vaccinations administered were received from 100% of GP practices in 2024 to 2025.

Vaccine uptake was 70.3% in adults aged 65 years and older (compared with 72.5% in 2023 to 2024) and 36.8% for those aged 6 months to under 65 years of age with 1 or more underlying clinical risk factors, compared with 39.1% in 2023 to 2024. Vaccine coverage in pregnant women is measured using a survey of pregnant women giving birth each year during January. Overall uptake in pregnant women was 62.1% compared with 60.9% in 2023 to 2024.

In health care workers, uptake reached 34.4% in the 2024 to 2025 season compared with 40.5% in the 2023 to 2024 season.

Influenza vaccine programme for children

England

The influenza vaccine uptake in 2 and 3 year olds in England is monitored by UKHSA throughout the season, through weekly and monthly extracts from GP system suppliers via ImmForm.

Cumulative vaccine uptake on influenza vaccinations administered up to 28 February 2025 was reported from 99.2% (6,177 out of 6,225) of GP practices in England in the 2024 to 2025 season. Comparative data is up to 29 February 2024 where vaccine uptake was reported from 93.6% (5,934 out of 6,342) of GP practices in England in the 2023 to 2024 season.

This season saw a vaccine uptake for all GP-registered 2 year olds of 41.7% (compared with 44.1% in the 2023 to 2024 season) and was 43.5% in 3 year olds (compared with 44.6% in the 2023 to 2024 season). The combined uptake for 2 and 3 year olds was 42.6% compared with 44.4% in the 2022 to 2023 season.

In school-aged children, the programme was mainly delivered via a school-based route. Uptake of seasonal influenza vaccine is monitored monthly by UKHSA throughout the season, through manual ImmForm collections provided by local teams for their responsible population.

An estimated 4,075,008 out of 8,111,462 eligible children in school years reception to year 11 in England received at least one dose of influenza vaccine during the period 1 September 2024 to 31 January 2025. The overall uptake was 50.2% compared with 49.9% in the 2023 2024 season. Vaccine uptake in all primary school age children (age 4 to 11 years old) was 54.5% compared with 55.1% in the 2023 to 2024 season. Vaccine uptake in secondary school age children (age 11 to 16 years old) was 44.6% compared with 42.8% in the 2023 to 2024 season.

Vaccine uptake in children of school age generally decreases with increasing age. This trend has been seen in the previous seasons.

Further detail on final influenza vaccine uptake data in school-aged children in England is available on GOV.UK.

Scotland

In Scotland, the uptake of seasonal influenza vaccine in children is recorded via the Vaccine Management Tool, with data accessed through the National Clinical Data Store (NCDS). During the season, PHS publishes weekly updates on the Public Health Scotland - Vaccination Surveillance Dashboard for those eligible in the following cohorts: 6 months to 2 years at risk, 2 to 5 years not at school, primary, and secondary school pupils.

The estimated uptake in preschool children (2 to under 5 years old, not yet in school) was 50.3% – this compares with 48.8% in the 2023 to 2024 season. For primary school children the estimated uptake was 68.1% compared with 69.0% in the 2023 to 2024 season. In secondary school children there was an estimated uptake of 53.1% compared with 52.9% in the 2023 to 2024 season. Note, caution should be taken when comparing uptake percentages between the seasons due to differences in data collection methods.

Northern Ireland

Vaccinations administered as part of the schools influenza vaccination programme are recorded on the Northern Ireland Child Health System (CHS) which feeds into VMS. Vaccinations administered by GP to children are recorded in VMS.

In 2024 to 2025 the childhood influenza vaccination programme continued to include all pre-school children aged 2 to 4 years old, all primary school aged children (years 1 to 7) and post primary school children in years 8 to 12. Pre-school children were offered vaccination through primary care, and primary and post-primary school children are offered vaccination through school health teams.

The vaccination uptake in 2024 to 2025 for pre-school children aged 2 to 4 years old was 30.0% (compared with 32.9% in 2023 to 2024). The vaccination uptake for children in primary school (aged approximately 4 to 11 years old) was 64.8% (compared with 68.6% in 2023 to 2024). Vaccine uptake in post-primary school children (years 8 to 12) was 58.8%, compared with 56.5% in 2023 to 2024. These year groups were vaccinated through school clinics and a small number by GP.

Wales

In Wales, immunisations for 2 and 3 year olds were mainly delivered through general practices. National uptake of influenza vaccine in 2 and 3 year olds increased slightly in 2024 to 2025. Uptake of influenza vaccine for children aged 2 years was 43.2% (compared with 41.3% in 2023 to 2024), for 3 year olds it was 44.0% (compared with 44.1% in 2023 to 2024). For the whole group of children aged 2 and 3 years, uptake was 43.6% (compared with 42.8% in 2023 to 2024). Further details will be published at the end of June.

The childhood influenza programme in Wales includes all primary and secondary school children. Uptake in school children remained stable. Uptake in primary school children was 61.6% (compared with 61.9% in 2023 to 2024). Uptake in secondary school children was 51.9% (compared with 49.7% in 2023 to 2024).

Vaccine effectiveness

Vaccine effectiveness against influenza presenting in primary care

In England, Scotland, Northern Ireland and Wales for the 2024 to 2025 season, influenza vaccine effectiveness (VE) was estimated using a test-negative study design. VE is presented against influenza in those presenting within primary care with symptoms of acute respiratory infection. Infection data were collected through 4 sentinel GP-based swabbing schemes in England (RCGP), Scotland (CARI), Northern Ireland and Wales (as described in the microbiological surveillance section of this report). Vaccination status of study participants was obtained through questionnaire at the time of swabbing (Wales) or data linkage with immunisation databases (England, Scotland, Northern Ireland).

In children aged 2 to 17 years, the overall adjusted influenza vaccine effectiveness (VE) in the 2024 to 2025 season was 55.6% (95% confidence interval (CI): 48.7% to 61.5%) against all laboratory confirmed influenza (Figure 55). In adults aged 18 to 64 years, the overall VE was 51.7% (95% CI: 45.6% to 57.1%) against all laboratory confirmed influenza. In adults aged 65 years and over, the overall VE was 36.6% (95% CI: 23.6% to 47.4%).

In subtype-specific analyses across the age groups, moderate VE was demonstrated against influenza A(H1N1) and A(H3N2). Protection against influenza B was good across all age groups.

Figure 55. Adjusted vaccine effectiveness against acute respiratory infection presentation in primary care with laboratory-confirmed influenza, by influenza subtype and age group, England, Scotland, Northern Ireland and Wales, 2024 to 2025 season [note 14] [note 15]

Note 14: Adjusted for week of sample, age group, sex, nation, clinical risk status.

Note 15: Numbers of cases and controls informing this analysis can be found in the supplementary data file.

Vaccine effectiveness against hospitalization

England

In England for the 2024 to 2025 season influenza VE was also estimated using a test-negative study design against hospitalization. VE is presented against influenza in those requiring hospitalisation with a diagnosis consistent with acute respiratory infection in England during the period week 40 2023 to week 13 2024. Infection and admission data was collected through SGSS, the Respiratory DataMart surveillance scheme and Secondary Uses Service (SUS) data. Vaccination status of study participants was obtained through data linkage with the Immunisation Information System (IIS).

In children aged 2 to 17 years, the overall adjusted VE in the 2024 to 2025 season was 62.2% (95% CI: 58.6% to 65.5%) against all laboratory confirmed influenza. In adults aged 18 to 64 years, the overall VE was 46.1% (95% CI: 42.7% to 49.3%) against all laboratory confirmed influenza. In adults aged 65 years and over, the overall VE was 40.5% (95% CI: 37.8% to 43.1%).

A proportion of influenza A positive samples were further subtyped, and VE was estimated against influenza A(H1N1) and A(H3N2). There was greater uncertainty in subtype-specific VE analyses across the age groups, especially against A(H3N2). Moderate VE was demonstrated against A(H1N1) for all age groups. VE against influenza A(H3N2) was highest in children aged 2 to 17 years, and lowest in adults aged 18 to 64 years where confidence intervals were close to zero. Protection against influenza B was good across all age groups (Figure 56).

Figure 56. Adjusted vaccine effectiveness against hospitalisation with a diagnosis consistent with an acute respiratory infection and laboratory-confirmed influenza by influenza subtype and age group, England, 2024 to 2025 season [note 15] [note 16]

Note 15: Numbers of cases and controls informing this analysis can be found in the supplementary data file.

Note 16: Adjusted for week of sample, age group, UKHSA region, clinical risk status.

Scotland

In Scotland, in the 2024 to 2025 season, VE was measured using a test-negative study design. VE is presented against influenza hospitalisation among individuals admitted to hospital, as an emergency admission, with a respiratory related diagnosis as main cause of admission. The analysis was performed through the data linkage of influenza testing data from the Electronic Communication of Surveillance in Scotland (ECOSS), hospital admission data from Scottish Morbidity Records 01 database and vaccination status of patients from the national clinical data store (NCDS). Included admissions were from 1 October 2024 until 11 April 2025.

In children aged 2 to 17 years receiving the live attenuated influenza vaccine (LAIV), the overall adjusted influenza vaccine effectiveness (aVE) in 2024 to 2025 was 74.9% (95% CI: 55.2% to 85.9%) against all laboratory-confirmed influenza in those admitted to hospital with a respiratory diagnosis. In adults aged 18 to 64 years, the overall aVE was 49.7% (95% CI: 40% to 57.8%), and in adults aged 65 years and over, the overall aVE was 38.2% (95% CI: 31.1% to 44.6%).

In type-specific analyses, aVE against influenza A in ages 2 to 17 years was 72.6% (95% CI: 50.2% to 84.9%), in 18 to 64 years it was 46.9% (95% CI: 36.4% to 55.7%), and in 65 years and above it was 37.7% (95% CI 30.5% to 44.2%). Similarly, aVE against influenza B in ages 2 to 17 years was 87.6% (95% CI: 5.2% to 98.4%), in 18 to 64 years it was 80.1% (95% CI: 53.2% to 91.6%), and in 65 years and above it was 63.5% (95% CI: 15.3% to 84.3%). When carrying out subtype analysis, aVE against influenza A(H1N1)pdm09 for those aged 2 to 17 years was 74.9% (95% CI: 36.4% to 90.1%), in 18 to 64 years it was 58.2% (95% CI: 25.2% to 76.6%), and in 65 years and above it was 40.4% (95% CI: 13.6% to 58.9%).

Figure 57. Adjusted vaccine effectiveness against hospitalisation with a diagnosis consistent with an acute respiratory infection and laboratory-confirmed influenza by influenza subtype and age group, Scotland, 2024 to 2025 season [note 17] [note 18]

Note 17: Adjusted for time during season, age, sex, deprivation and number of clinical risk groups.

Note 18: it was not possible to estimate vaccine effectiveness against influenza A(H3N2) in those aged between 2 and 17 years, and adults aged 18 to 64 years due to low case numbers.

Hospital admissions averted through vaccination

The number of hospital admissions averted, in England, due to the influenza vaccination programme during the 2024 to 2025 season was estimated by fitting an age and risk-stratified dynamic influenza transmission model to surveillance data. The model was fitted to GP ILI consultation data from RCGP and hospital admissions data from SARI Watch. Additional model data included: virology samples for swabbed patients from RCGP, vaccine uptake data from ImmForm, vaccine effectiveness against hospital admissions from the 2024 to 2025 VE estimates and population data from the 2023 mid-year population estimates for England. The model distinguished between VE against infection and VE against hospitalisation, with VE against infection an inferred parameter based on data from SARS-CoV-2, influenza A/B and respiratory syncytial virus positivity and association with influenza-like illness and self-reported symptoms, over the 2022 to 2023 winter season in the UK: A longitudinal surveillance cohort. The possibility of lower VE against infection was explored as a sensitivity analysis.

The model was fitted to all available surveillance data. After fitting, the model was used to explore how removing the entire vaccination programme would impact hospital admissions and to estimate the number of hospital admissions averted through vaccination. The model output indicated that an estimated 96,000 to 120,200 hospital admissions were averted due to the influenza vaccination programme in the 2024 to 2025 season. In the sensitivity analysis, with reduced VE against infection, an estimated 33,200 to 52,400 hospital admissions were averted.

Further details of the influenza transmission model, and previous seasons’ results, are available in Influenza hospital admissions prevented by vaccination: a transmission dynamic analysis of the 2022 to 2023 and 2023 to 2024 programmes in England.

Avian and other zoonotic influenza

Avian influenza A(H5N1)

From January 2003 to January 2025, a total of 964 human cases of avian influenza A(H5N1) have been reported globally. Of these cases, 466 were fatal, resulting in a case fatality rate of 48%. Since 2020, clade 2.3.4.4b of avian influenza A (H5N1) has become widespread in birds, with some occasional spillover to non-avian species and rare detections in humans.

On 25 March 2024, the US reported an outbreak of avian influenza A(H5N1) clade 2.3.4.4b, genotype B3.13 in dairy cattle, marking the first documented instance of influenza A virus infection in this species. The first human case linked to this incident had direct exposure to presumed-infected cattle on a commercial dairy farm in Texas. A second human case was reported on 22 May 2024 in Michigan, also following exposure to infected dairy cows. The outbreak remains ongoing, with genotype B3.13 confirmed in dairy cattle across 17 US states. This genotype has not been detected in birds or mammals outside the US.

As of 30 April 2025, a total of 70 human cases of avian influenzas A(H5N1) have been reported in the US since 2024. Of these, 41 cases were associated with exposure to infected dairy cattle, 24 cases with involvement in poultry depopulation, two cases were linked to backyard poultry exposure, and three cases had unknown exposures at the time of reporting. The majority of cases experienced mild symptoms, such as conjunctivitis and upper respiratory infections. Two cases developed severe illness requiring hospitalisation. One fatality was reported in 2025, making this the first death attributed to A(H5N1) in the US. Virological analyses have identified genotypes B3.13 and D1.1 among these cases. Genotype B3.13 has been commonly identified in cattle outbreaks with spillover cases in humans, while genotype D1.1 has been detected in poultry, wild birds, and some cattle and has also been associated with human infections. Another genotype D1.2 was detected in 2024 in pigs on a non-commercial farm in Oregon. Genomic analysis has shown the transmission from local migratory birds. Currently, there is no evidence of human-to-human transmission associated with these cases.

Between January 2024 and May 2025, Cambodia reported 13 confirmed human cases of A(H5N1), including five deaths. Most cases were associated with direct contact with infected poultry. In 2024, two cases, including a young child, died after direct exposure to infected poultry. In 2025, three additional deaths were reported. All infections were attributed to clade 2.3.2.1c, with no evidence of human-to-human transmission. The most recent fatal case was reported in March 2025, a three-year-old boy from Kratie province who died from the infection. Investigations confirmed exposure to infected poultry.

On 27 January 2025, a human case of A(H5N1) was confirmed in the West Midlands region of the UK. The individual acquired the infection through close contact with infected birds on a farm. The avian samples tested positive for clade 2.3.4.4b, specifically the D1.2 genotype, which is genetically distinct from the strains currently circulating among mammals and birds in the US. This was the first human case in the UK since 2024. Prior to this, an enhanced surveillance study conducted since 2023 identified five asymptomatic detections of clade 2.3.4.4b in workers exposed to infected poultry.

Other avian influenza subtypes

There has been an increase in detections of both influenza A(H5N6) and influenza A(H9N2) in humans globally, with sporadic cases continuing to be reported. Between 2014 to May 2025, a total of 93 laboratory-confirmed human cases of influenza A(H5N6) have been reported, with the most recent case reported in China. Since 2015, 117 confirmed cases of A(H9N2) have been reported globally, including two deaths. As of 24 May 2025, a total of 99 laboratory-confirmed human cases of A(H9N2), have been reported, with an additional four cases identified in China between December 2024 and January 2025. All recent cases were linked to poultry exposure and there were no associated fatalities. One additional case was reported from Vietnam, with symptom onset in March 2024.

Most human cases of avian influenza viruses are exposed through contact with infected poultry or contaminated environments, including live poultry markets or domestically kept birds. Since the viruses continue to be detected in animals and environments, further human cases can be expected. However, the current epidemiological and virological evidence suggests that these viruses have not acquired the ability to undergo sustained transmission among humans. It is important to ensure that imported cases of suspected avian influenza are detected promptly to ensure public health measures including infection control can be rapidly put in place to minimise any risk of onward transmission.

Swine influenza zoonoses

In March 2024, the US reported its first human case of swine influenza A (H1N2)v virus of the year, involving a child with a history of contact with pigs. The child was hospitalized and subsequently recovered. There was no evidence of human-to-human transmission. As of April 10, 2025, no additional human cases of swine influenza have been reported in the UK beyond a single case of influenza A(H1N2)v clade 1 B.1.1, identified in England in November 2023.

Globally, sporadic human infections with swine influenza viruses continue to occur, including influenza A(H3N2)v, influenza A(H1N1)v, and influenza A(H1N2)v. Close contact with infected pigs, or visits to settings such as farms and agricultural fairs, remains a recognised exposure risk.

Data sources and methodology

For additional information regarding data sources please refer to the data quality report for national flu and COVID-19 surveillance.

Further details on the data from Scotland informing this report can be found in the weekly report, a methodology and metadata supplementary datafile. In addition, there are further resources on the CARI sentinel surveillance.

Further details on the data from Northern Ireland informing this report are available in the weekly report as well specific further details on vaccine coverage data.

Further details on the data from Wales informing this report are available in the weekly report.

Further information and contact details

Feedback and contact information

To provide feedback and for all queries relating to this document, please contact respdsr.enquiries@ukhsa.gov.uk

Acknowledgements

Compiled by the Influenza surveillance section, Immunisation and Vaccine-Preventable Diseases Division, UK Health Security Agency with contributions from:

• Public Health Scotland
• Public Health Wales
• Public Health Agency, Northern Ireland
• Royal College of General Practitioners
• Real-time Syndromic Surveillance team, UK Health Security Agency
• Respiratory Virus Unit, Colindale, UK Health Security Agency

Official statistics designation

Our statistical practice is regulated by the Office for Statistics Regulation (OSR). OSR sets the standards of trustworthiness, quality and value in the Code of Practice for Statistics that all producers of official statistics should adhere to.

You are welcome to contact us directly by emailing respdsr.enquiries@ukhsa.gov.uk with any comments about how we meet these standards.

Alternatively, you can contact OSR by emailing regulation@statistics.gov.uk or via the OSR website.

UKHSA is committed to ensuring that these statistics comply with the Code of Practice for Statistics. This means users can have confidence in the people who produce UKHSA statistics because our statistics are robust, reliable and accurate. Our statistics are regularly reviewed to ensure they support the needs of society for information.