Seasonal influenza - Annual Epidemiological Report for 2022/2023

The 2022/2023 influenza season marked the return of influenza virus activity at almost pre-pandemic levels in the EU/EEA countries. This season was characterised by an earlier start of the seasonal epidemic and an earlier peak in positivity compared to the four previous seasons.

The percentage of positive specimens peaked at 42% in week 51/2022, followed by a decrease until week 4/2023 when it reached 22% positivity before rising again to fluctuate around 28% positivity between week 5−12/2023. The threshold of <10% positivity was passed in week 17, indicating the end of the seasonal influenza epidemic.

Overall, influenza A(H3N2) viruses dominated in sentinel primary care specimens, however higher circulations of A(H1N1)pdm09 (from week 50/2022) and type B viruses (from week 2/2023) were observed. In non-sentinel specimens, A(H3N2) dominated over A(H1N1)pdm09 viruses. Both influenza type A and type B viruses have been detected in hospitalised patients in ICUs and other wards, with influenza type A the dominant type. Similarly, influenza type A viruses have been dominant among SARI patients. 

The majority of genetically characterised influenza viruses fell within clades of the recommended vaccine components. Interim vaccine effectiveness estimations for the 2022−2023 season have been reported by the ECDC Vaccine Effectiveness, Burden and Impact Studies (VEBIS) multi-country network, with data collected from 16 European countries from 3 October 2022 to 31 January 2023. These interim results indicate a  ≥27% and a ≥50% reduction in disease occurrence among all-age influenza vaccine recipients for influenza A and B, respectively during the 2022−2023 influenza season. Very few influenza viruses with antiviral resistance were reported.