Timing of influenza seasons
Updated 14 February 2024
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Weekly rates of GP consultations for influenza-like illness (ILI) in England are collected through the Research and Surveillance Centre (RSC) of the Royal College of General Practitioners (RCGP). The RCGP has an extensive network of GP practices throughout England. Data on the number of ILI consultations is extracted from these practices on a weekly basis.
The data presented below shows influenza seasonality. The timing and length of an influenza season varies greatly between seasons.
The lines represent weeks when the GP ILI activity was above the baseline threshold level. The squares represent the week when flu is seen to peak based on highest ILI activity in a given season. In seasons where the ILI consultation rate did not exceed the baseline threshold, only a square for the peak week is shown.
Influenza seasonality was disrupted in 2009 due to the influenza A/H1N1 pandemic, and in 2020 to 2022 due to coronavirus (COVID-19) pandemic control measures. COVID-19 and other respiratory viruses can also contribute to ILI reporting from primary care. Influenza was very low in 2020 to 2021 and no peak is reported here. In 2022 to 2023, GP ILI activity was consistent with the 2019 to 2020 season with week 51 reported as the ILI peak, as this is the peak in GP ILI activity that coincided with other influenza surveillance activity.
Figure 1: GP influenza-like illness consultation activity in England, 1988 to 1989 season to 2022 to 2023 season
Figure 1 shows a graph of GP ILI consultation activity in England between weeks 40 and 20 each influenza season from the 1988 to 1989 season to the 2022 to 2023 season. Each season shows a line representing weeks when the GP ILI activity was above the baseline threshold level. Each season shows a square representing the week in which influenza activity peaked each season. The figure shows the timings and length of influenza seasons varying from season to season. The start of the above baseline activity varies from week 42 to week 7. The end of above baseline activity varies from week 49 to week 15. Peak activity varies from week 43 to week 13.