Influenza A(H3N2) Subclade K (J.2.4.1): Molecular Characterization, Antigenic Divergence, and Global Spread During the 2025/26 Season [PDF]
Infectious Disease ReportsBackground: Influenza A(H3N2) continues to evolve rapidly, frequently eroding population immunity and challenging seasonal vaccine strain selection. During the 2025/26 season, the A(H3N2) subclade K (J.2.4.1) expanded quickly across multiple regions and ...
Francesco Branda +5 more
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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 [PDF]
EurosurveillanceDuring 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 ...
Hanna Nohynek
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Northern Hemisphere 2025/26 influenza vaccine effectiveness during months with influenza A(H3N2) subclade K predominance— Suzhou, Eastern China [PDF]
International Journal of Infectious DiseasesDuring this 2025/26 Northern Hemisphere influenza season, the predominant influenza A(H3N2) subclade K virus has binding site mutations and postvaccine sera reduced inhibition, raising concerns about antigenic differences with available vaccines.
Pengwei Cui +18 more
doaj +4 more sources
Interim 2025/26 influenza vaccine effectiveness estimates with immuno-epidemiological considerations for A(H3N2) subclade K protection, Canada, January 2026 [PDF]
EurosurveillanceIn interim 2025/26 analyses, the Canadian Sentinel Practitioner Surveillance Network estimates influenza vaccine reduced the risk of medically-attended acute respiratory illness due to predominant influenza A(H3N2) viruses, including antigenically ...
Danuta M Skowronski
doaj +4 more sources
Eurosurveillance[This article was retracted on 19 February 2026.] During the early 2025/26 influenza season, influenza A(H3N2) subclade K rapidly predominated in Beijing, China.
Peng Yang
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Cross-sectional study on protective antibodies against influenza A virus subtypes and cross-protection against influenza A(H3N2) subclade K, Portugal, August 2025 [PDF]
EurosurveillanceThe 2025/26 season was marked by co-circulation of influenza A subtypes, with the first detection of A(H3N2) subclade K in September 2025. In August 2025 in Portugal, 14.8% (95% CI: 12.2–17.8) of 886 persons tested had cross-protective antibodies against
Ana Paula Rodrigues
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Influenza A(H3N2) subclade K (J.2.4.1) viruses associated with a surge at a university health clinic, Arizona, the United States, November to early December 2025 [PDF]
EurosurveillanceGenomic surveillance during an influenza surge between November and early December 2025 at a university health clinic in the United States identified A(H3N2) subclade K (J.2.4.1) viruses with shared haemagglutinin amino acid substitutions in antigenic ...
Vel Murugan
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Population immunity, post-vaccine and post-infection antibody responses to influenza A (H3N2) subclade J.2 and K (J.2.4.1) viruses, Hong Kong, 2025 [PDF]
EurosurveillanceWe assessed haemagglutination inhibition (HAI) antibody titres against 2025 influenza A(H3N2) J.2 vaccine reference viruses and the novel subclade K (J.2.4.1) in age-stratified Hong Kong sera (collected May–July 2025), vaccine recipients and sera from ...
Malik Peiris
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Influenza A(H3N2) subclade K (J.2.4.1): epidemiology in Asia, clinical context, and the “superflu” framing [PDF]
New Microbes and New InfectionsTimotius Ivan Hariyanto
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Host cell entry and neutralisation sensitivity of H3N2 influenza A virus subclade K [PDF]
npj VaccinesIn 2025, a mutated H3N2 lineage, subclade K, emerged, showing high activity in many regions. Mutations in the hemagglutinin (HA) may affect cell entry and antibody-mediated neutralisation.
Nicole Moor +11 more
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