Niina Ikonen, Anu Haveri, Erika Lindh, Oona Liedes, Saimi Vara, Sari H. Pakkanen, Anu Kantele, Tea Nieminen, Veli-Jukka Anttila, Hanna Välimaa, Merit Melin, Carita Savolainen-Kopra, Hanna Nohynek
During autumn 2025, drifted influenza A(H3N2) subclade K and A(H1N1)pdm09 subclade D.3.1. and D.3.1.1 viruses were detected in Finland. We assessed antibody responses against 2024/25 vaccine and 2025/26 epidemic influenza A strains among 46 Finnish healthcare workers before and after influenza vaccination with the 2024/25 vaccine; this vaccine included identical A(H1N1)pdm09 but different A(H3N2) strains compared with the 2025/26 vaccine. Neutralising antibody responses were markedly reduced against the A(H3N2) subclade K virus and titres for certain A(H1N1)pdm09 strains were reduced.