Reduced neutralising antibody responses against emerging 2025/26 influenza A(H1N1)pdm09 subclade D.3.1 and A(H3N2) subclade K viruses among healthcare workers, Finland, August to October 2025

Eurosurveillance 2026 Open access

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Authors: 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
+1 more Hanna Nohynek
DOI: 10.2807/1560-7917.es.2026.31.6.2600094
Cited by: 4
References: 12

Abstract

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.

Fields of Study & Subjects

Influenza Virus Research Studies Respiratory viral infections research SARS-CoV-2 and COVID-19 Research

Publication details

Journal / source
Eurosurveillance
Publisher
European Centre for Disease Control and Prevention (ECDC)
Volume
31
Issue
6
Publication date
12 February 2026
Language
EN