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
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.
Authors
- Saimi Vara
- Merit Melin (ORCID: https://orcid.org/0000-0001-9375-4327)
- Hanna Välimaa
- Anu Haveri (ORCID: https://orcid.org/0000-0003-4620-7536)
- Tea Nieminen (ORCID: https://orcid.org/0000-0003-2157-4567)
- Oona Liedes (ORCID: https://orcid.org/0009-0007-1570-4325)
- Niina Ikonen (ORCID: https://orcid.org/0000-0003-0724-8888)
- Anu Kantele (ORCID: https://orcid.org/0000-0002-0004-1000)
- Sari H. Pakkanen (ORCID: https://orcid.org/0000-0003-4522-5337)
- Hanna Nohynek
- Erika Lindh
- Carita Savolainen-Kopra
- Veli-Jukka Anttila
Institutions
- University of Helsinki (FI)
- Helsinki University Hospital (FI)
- Finnish Institute for Health and Welfare (FI)
- Helsinki Children's Hospital (FI)
- Hospital District of Helsinki and Uusimaa (FI)
Publication Details
- Journal
- Eurosurveillance
- Published
- 2026-02-12
- DOI
- https://doi.org/10.2807/1560-7917.es.2026.31.6.2600094
- Primary Topic
- Influenza Virus Research Studies
- Type
- article
- Field-Weighted Citation Impact
- 0.00