Influenza virus characterization - Summary Europe, December 2023

Surveillance report
Publication series: Influenza Virus Characterisation

Influenza virus characterization: summary report, Europe, December 2023. Copenhagen: WHO Regional Office for Europe and Stockholm: European Centre for Disease Prevention and Control; 2023. Licence: CC BY 3.0 IGO.

Genetic and antigenic characterization data generated at the Worldwide Influenza Centre for viruses with collection dates after 31 January 2023 until 31 August 2023 informed the WHO influenza vaccine composition meeting (VCM) in September 2023 when recommendations were made for the southern hemisphere (SH) 2024 influenza season. At the September 2023 VCM it was recommended to change the A(H1N1)pdm09 and A(H3N2) vaccine components for the 2024 SH season. Previously, at the February 2023 VCM, which focused on data from viruses collected after 31 August 2022 until 31 January 2023, it was also recommended to change the A(H1N1)pdm09 vaccine component for the 2023‑2024 northern hemisphere (NH) season.

Executive Summary

It is recommended vaccines for use in the 2024 SH influenza season contain the following:

Trivalent: Egg‑based Vaccines
• an A/Victoria/4897/2022 (H1N1)pdm09‑like virus;
• an A/Thailand/8/2022 (H3N2)‑like virus; and
• a B/Austria/1359417/2021 (B/Victoria lineage)‑like virus.

Trivalent: Cell‑ or recombinant‑based Vaccines
• an A/Wisconsin/67/2022 (H1N1)pdm09‑like virus;
• an A/Massachusetts/18/2022 (H3N2)‑like virus; and
• a B/Austria/1359417/2021 (B/Victoria lineage)‑like virus.

Quadrivalent (egg‑ or cell culture‑ or recombinant‑based vaccines): Above 3 components; and a B/Phuket/3073/2013 (B/Yamagata lineage)‑like virus.

Influenza B/Yamagata‑lineage
No B/Yamagata‑lineage viruses with collection dates after March 2020 have been detected or sequences released in GISAID as of 15 December 2023.

The absence of confirmed detection of naturally occurring B/Yamagata lineage viruses is indicative of very low risk of infection by B/Yamagata lineage viruses. Therefore, it is the opinion of the WHO influenza vaccine composition advisory committee that inclusion of a B/Yamagata lineage antigen in quadrivalent influenza vaccines is no longer warranted, and every effort should be made to exclude this component as soon as possible. A continued effort by all NICs of GISRS is required to identify /Yamagata‑lineage viruses for detailed characterization to determine if there are any in circulation.