OFFLU Avian Influenza Matching (AIM) Report, October 2023

This document provides an October 2023 OFFLU-AIM report that synthesises epidemiological, genetic and antigenic evidence on Gs/Gd-lineage H5Nx—focusing on clades 2.3.4.4b, 2.3.2.1a and “2.3.2.1c”—to assess vaccine–virus match (via chicken antisera HI data and antigenic cartography), summarise regional findings and trial results, and offer practical guidance (with annexes) for monitoring vaccine performance and prioritising vaccine antigen updates.