Flu levels low at start of season but higher than previous 4 years
With possible signs of an early flu season, UKHSA urges those eligible to get vaccinated.
UK Health Security Agency (UKHSA) has published the first of its weekly winter respiratory virus surveillance reports, based on a range of indicators provided by GPs, hospitals, laboratories and the wider community.
The surveillance report for week 40 (28 September and 4 October 2026) shows:
- influenza activity increased and is circulating at baseline levels
- flu positivity increased with a positivity rate of 6.5% compared with 5% on the previous week
- overall, flu hospitalisations were 1.97 per 100,000. This surveillance formally starts in week 40 so a comparison to the previous week is not possible
Flu activity throughout September has been higher than in the same period during all past 4 winter seasons. While still at baseline (very low) levels, flu trends have been rising since August and there are possible signs that we may see an early flu season.
The report also shows:
- the increases in flu are being driven by young adults
- COVID-19 activity is increasing and above baseline, although still at low levels
- the strains currently circulating, including those known as XFG, are closely related to strains seen here for over a year
- Rhinovirus activity, otherwise known as the cold common, has now started to decline after a sharp rise in activity in previous weeks
- Respiratory Syncytial Virus (RSV) activity remains at baseline levels with very low levels of the virus circulating
Flu viruses change every year, which is why flu vaccines are updated annually. Some years ‘drifted’ flu viruses occur, which means the virus that is circulating has continued to evolve and has some genetic changes from the one that was used to make the vaccine.
A recent World Health Organization (WHO) technical report has indicated that one of the flu A(H1N1) viruses that has recently been seen at low levels in Europe, and recently in the UK, has ‘drifted’ compared to the virus component used in this year’s flu vaccine. Last year we also saw a ‘drifted’ A(H3N2) flu virus, but the vaccines still gave good protection.
It is still too early in the season to say with any certainty whether this drifted A(H1N1) virus will circulate widely in the UK or how effective the vaccine will be against it. Flu is still at very low levels, but the subtyping data available so far this season shows there is an equal mix of subtypes A(H3N2) and A(H1N1) in England.
Importantly, the flu vaccine contains components to help protect against all 3 types of flu viruses (Flu A subtypes H1N1 and H3N2 - and Flu B). Flu is unpredictable, some seasons one flu virus will dominate, and some seasons all 3 flu viruses could circulate at different times during winter.
As we saw with last year’s A(H3N2) virus, which dominated, flu vaccines typically remain effective at preventing severe flu, even when drifted strains are seen.
Despite the drifted virus and an earlier start to the flu season last year, the overall level of cases over the course of the season was lower and with lower mortality estimates than the previous year. Modelling indicated that, in England last winter, the vaccination programme prevented around 100,000 hospital admissions and 7,000 deaths.
The composition of flu vaccines, developed by the WHO are adjusted each year, to account for any genetic changes and are designed to help protect against the viruses that are likely to be circulating during the forthcoming flu season. Decisions about which virus strains should be included are made several months before flu season begins, so manufacturers have time to produce enough stocks, but viruses can continue to change. This means that sometimes, by the time vaccines are delivered they aren’t always an exact match against the strains circulating.
Dr Jamie LopezBernal, Consultant Epidemiologist at UKHSA, said:
Flu levels are increasing with the possibility of an early flu season so now is the time for those eligible to get vaccinated.
The vaccine contains components to help protect against all three types of flu virus. We may see one flu virus dominating at different times during winter, or all three circulating at similar levels throughout. As we saw with last year’s dominant virus, flu vaccines typically remain effective at preventing severe flu, even when drifted strains are seen.
Today’s report on COVID-19 surveillance for week 40 also shows:
- COVID-19 activity increased and is circulating at low levels
- COVID-19 positivity increased with a weekly positivity rate of 9.1% compared with 7.9% in the previous week.
- COVID-19 hospitalisations increased to 2.04 per 100,000 compared with 1.75 per 100,000 in the previous week
- COVID-19 ICU admissions remained low at 0.06 per 100,000 compared with 0.05 per 100,000 in the previous week
Dr Alex Allen, Consultant Epidemiologist at UKHSA, said:
While COVID-19 activity has shown some recent increases, cases remain at low levels in the UK.
It’s completely normal for viruses to change over time. The strains currently going around, including those known as XFG, are closely related to strains that have been with us for over a year, so this isn’t something new. We’re also not seeing any evidence that these are making people more ill or spreading faster than before, and this year’s autumn vaccine has been specifically designed to protect against them.
If you are eligible for a COVID-19 vaccine it is because you are at greater risk of severe illness and being hospitalised. Don’t risk it, get the vaccine and give yourself the best protection.
Members of the public who are eligible for a free vaccine can check their eligibility and book an appointment through the NHS App, online, or by contacting their GP practice or a local pharmacy.
More information on eligibility is available on the UKHSA blog:
Your guide to who’s eligible for the autumn 2026 flu vaccine – UK Health Security Agency
Who’s eligible for the 2026 COVID-19 vaccine, or ‘Autumn Booster’? – UK Health Security Agency
What is RSV and who is eligible for the vaccine? – UK Health Security Agency