1887
  1. Home
  2. Eurosurveillance
  3. Volume 31, Issue 6, 12/Feb/2026
  4. Article
Rapid communication Open Access
Like 0
Download

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.

© Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.
Loading

Article metrics loading...

/content/10.2807/1560-7917.ES.2026.31.6.2600094
2026-02-12
2026-03-15
/content/10.2807/1560-7917.ES.2026.31.6.2600094
Loading
Loading full text...

Full text loading...

/deliver/fulltext/eurosurveillance/31/6/eurosurv-31-6-2.html?itemId=/content/10.2807/1560-7917.ES.2026.31.6.2600094&mimeType=html&fmt=ahah

References

  1. European Centre for Disease Prevention and Control (ECDC). Early estimates of seasonal influenza vaccine effectiveness against influenza requiring medical attention at primary care level in Europe, week 41 - 49, 2025. Stockholm: ECDC; 2025. Available from: https://www.ecdc.europa.eu/en/news-events/early-estimates-seasonal-influenza-vaccine-effectiveness-against-influenza-requiring
  2. World Health Organization (WHO). Recommended composition of influenza virus vaccines for use in the 2024-2025 northern hemisphere influenza season. Geneva: WHO; 23 Feb 2024. Available from: https://www.who.int/publications/m/item/recommended-composition-of-influenza-virus-vaccines-for-use-in-the-2024-2025-northern-hemisphere-influenza-season
  3. World Health Organization (WHO). Recommended composition of influenza virus vaccines for use in the 2025-2026 northern hemisphere influenza season. Geneva: WHO; 28 Feb 2025. Available from: https://www.who.int/publications/m/item/recommended-composition-of-influenza-virus-vaccines-for-use-in-the-2025-2026-nh-influenza-season
  4. Zhou B, Donnelly ME, Scholes DT, St George K, Hatta M, Kawaoka Y, et al. Single-reaction genomic amplification accelerates sequencing and vaccine production for classical and Swine origin human influenza a viruses. J Virol. 2009;83(19):10309-13.  https://doi.org/10.1128/JVI.01109-09  PMID: 19605485 
  5. Shepard SS, Meno S, Bahl J, Wilson MM, Barnes J, Neuhaus E. Viral deep sequencing needs an adaptive approach: IRMA, the iterative refinement meta-assembler. BMC Genomics. 2016;17(1):708.  https://doi.org/10.1186/s12864-016-3030-6  PMID: 27595578 
  6. Liedes O, Reinholm A, Ekström N, Haveri A, Solastie A, Vara S, et al. Influenza A(H5N8) vaccine induces humoral and cell-mediated immunity against highly pathogenic avian influenza clade 2.3.4.4b A(H5N1) viruses in at-risk individuals. Nat Microbiol. 2026;11(1):155-68.  https://doi.org/10.1038/s41564-025-02183-5  PMID: 41350922 
  7. Haveri A, Ikonen N, Savolainen-Kopra C, Julkunen I. Long-lasting heterologous antibody responses after sequential vaccination with A/Indonesia/5/2005 and A/Vietnam/1203/2004 pre-pandemic influenza A(H5N1) virus vaccines. Vaccine. 2021;39(2):402-11.  https://doi.org/10.1016/j.vaccine.2020.11.041  PMID: 33246672 
  8. Dapat C, Peck H, Jelley L, Diefenbach-Elstob T, Slater T, Hussain S, et al. Extended influenza seasons in Australia and New Zealand in 2025 due to the emergence of influenza A(H3N2) subclade K viruses. Euro Surveill. 2025;30(49):2500894.  https://doi.org/10.2807/1560-7917.ES.2025.30.49.2500894  PMID: 41383175 
  9. Kirsebom FC, Thompson C, Talts T, Kele B, Whitaker HJ, Andrews N, et al. Early influenza virus characterisation and vaccine effectiveness in England in autumn 2025, a period dominated by influenza A(H3N2) subclade K. Euro Surveill. 2025;30(46):2500854.  https://doi.org/10.2807/1560-7917.ES.2025.30.46.2500854  PMID: 41267661 
  10. Separovic L, Sabaiduc S, Zhan Y, Kaweski SE, Olsha R, Hasso M, et al. Interim 2025/26 influenza vaccine effectiveness estimates with immuno-epidemiological considerations for A(H3N2) subclade K protection, Canada, January 2026. Euro Surveill. 2026;31(5):2600068.  https://doi.org/10.2807/1560-7917.ES.2026.31.5.2600068  PMID: 41645799 
  11. Haveri A, Ikonen N, Kantele A, Anttila VJ, Ruotsalainen E, Savolainen-Kopra C, et al. Seasonal influenza vaccines induced high levels of neutralizing cross-reactive antibody responses against different genetic group influenza A(H1N1)pdm09 viruses. Vaccine. 2019;37(20):2731-40.  https://doi.org/10.1016/j.vaccine.2019.03.078  PMID: 30954308 
  12. De Clercq A, Blanquart F, Vieillefond V, Visseaux B, Jacques A, Haim-Boukobza S, et al. Interim vaccine effectiveness against influenza virus among outpatients, France, October 2025 to January 2026. Euro Surveill. 2026;31(2):2500992.  https://doi.org/10.2807/1560-7917.ES.2026.31.2.2500992  PMID: 41540925 
  13. Saubi N, Andrés C, Prats-Méndez I, González-Sánchez A, Davtyan A, Vásquez-Mercado R, et al. Expansion of influenza A(H1N1)pdm09 NA:S247N viruses with reduced susceptibility to oseltamivir, Catalonia, Spain, and in Europe, July to October 2025. Euro Surveill. 2025;30(48):2500873.  https://doi.org/10.2807/1560-7917.ES.2025.30.48.2500873  PMID: 41346317 
  14. Smith DJ, Lapedes AS, de Jong JC, Bestebroer TM, Rimmelzwaan GF, Osterhaus ADME, et al. Mapping the antigenic and genetic evolution of influenza virus. Science. 2004;305(5682):371-6.  https://doi.org/10.1126/science.1097211  PMID: 15218094 
  15. Koel BF, Burke DF, Bestebroer TM, van der Vliet S, Zondag GCM, Vervaet G, et al. Substitutions near the receptor binding site determine major antigenic change during influenza virus evolution. Science. 2013;342(6161):976-9.  https://doi.org/10.1126/science.1244730  PMID: 24264991 
  16. European Centre for Disease Prevention and Control (ECDC). Threat assessment brief – Assessing the risk of influenza for the EU/EEA in the context of increasing circulation of A(H3N2) subclade K. Stockholm: ECDC; 20 November 2025. Available from: https://www.ecdc.europa.eu/en/publications-data/threat-assessment-brief-assessing-risk-influenza-november-2025
  17. Sabaiduc S, Kaweski SE, Separovic L, Gao R, Ranadheera C, Bastien N, et al. Emergence of seasonal influenza A(H3N2) variants with immune escape potential warrants enhanced molecular and epidemiological surveillance for the 2025-2026 season. J Assoc Med Microbiol Infect Dis Can. 2025;10(4):281-98.  https://doi.org/10.3138/jammi-2025-0025 
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
<p class="citation"> <span>Citation style for this article:</span> <span class="meta-value authors"> <a href="/search?value1=Niina+Ikonen&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Ikonen Niina</a>, <a href="/search?value1=Anu+Haveri&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Haveri Anu</a>, <a href="/search?value1=Erika+Lindh&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Lindh Erika</a>, <a href="/search?value1=Oona+Liedes&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Liedes Oona</a>, <a href="/search?value1=Saimi+Vara&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Vara Saimi</a>, <a href="/search?value1=Sari+H+Pakkanen&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Pakkanen Sari H</a>, <a href="/search?value1=Anu+Kantele&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Kantele Anu</a>, <a href="/search?value1=Tea+Nieminen&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Nieminen Tea</a>, <a href="/search?value1=Veli-Jukka+Anttila&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Anttila Veli-Jukka</a>, <a href="/search?value1=Hanna+V%C3%A4limaa&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Välimaa Hanna</a>, <a href="/search?value1=Merit+Melin&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Melin Merit</a>, <a href="/search?value1=Carita+Savolainen-Kopra&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Savolainen-Kopra Carita</a>, <a href="/search?value1=Hanna+Nohynek&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Nohynek Hanna</a></span>. 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. <a href="/content/ecdc">Euro Surveill.</a> 2026;31(6):pii=2600094. <a href="https://doi.org/10.2807/1560-7917.ES.2026.31.6.2600094" title="doi link" target="_blank">https://doi.org/10.2807/1560-7917.ES.2026.31.6.2600094</a> <span class="ES_Article_citation"> <span class="generated">Received</span>: 02 Feb 2026;&nbsp;&nbsp; <span class="generated">Accepted</span>: 10 Feb 2026 </span> </p>
/content/10.2807/1560-7917.ES.2026.31.6.2600094
/content/10.2807/1560-7917.ES.2026.31.6.2600094
Loading

Data & Media loading...

Supplementary data

Submit comment
Close
Comment moderation successfully completed
This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error