Influenza virus characterization: summary report, Europe, February 2023

Overview

The December 2022 characterisation report , was the third report for the 2022-2023 influenza season. Currently, as of week 08/2023, 231 015 detections have been reported. This represents a 5.2-fold increase in detections compared to the same period of the 2021-2022 season, despite a modest decrease (4%) in the number of samples tested. Of the 2022-2023 detections, 84% were type A viruses, with A(H3N2) and A(H1N1)pdm09 viruses being detected in equal proportions overall, following a rise in the proportion of A(H1N1)pdm09 viruses detected in recent weeks. Since December, the proportion of detections being type B viruses has risen from 6% to 16% and all 3 371 viruses (9% of the total) ascribed to a lineage have been B/Victoria. The epidemic threshold (10% influenza positivity within sentinel specimens) was crossed in week 45/2022 and has remained above this to week 08/2023.