Influenza returns with a season dominated by clade 3C.2a1b.2a.2 A(H3N2) viruses, WHO European Region, 2021/22

In the WHO European Region, COVID-19 non-pharmaceutical interventions continued slowing influenza circulation in the 2021/22 season, with reduced characterisation data. A(H-3) predominated and, in some countries, co-circulated with A(H-1)pdmo9 and B/Victoria viruses. No B/Yamagata virus detections were confirmed. Substantial proportions of characterised circulating virus subtypes or lineages differed antigenically from their respective northern hemisphere vaccine components. Appropriate levels of influenza virus characterisations should be maintained until the season end and in future seasons, when surveillance is adapted to integrate SARS-CoV-2.

Automated summary

Non-pharmaceutical interventions for COVID-19 have continued to slow down the circulation of influenza in the WHO European Region in the 2021/22 season. The A(H-3) virus strain has dominated, co-circulating with A(H-1)pdmo9 and B/Victoria viruses in some countries. No detections of the B/Yamagata virus have been confirmed. Many of the circulating virus subtypes or lineages have shown antigenic differences from their respective vaccine components in the northern hemisphere. Adequate levels of influenza virus characterizations should be maintained until the end of the season and in future seasons, when surveillance is adapted to include SARS-CoV-2.