First detection and transatlantic introduction of Influenza A(H3N2) subclade K (J.2.4.1) into Ecuador: insights from genomic sentinel surveillance [PDF]
Frontiers in Public HealthBackgroundThe rapid evolution of Influenza A(H3N2) requires constant global monitoring. This study analyzes the genomic characteristics and the first introduction of the emerging subclade K (J.2.4.1) in Ecuador, utilizing publicly available data to trace
Alfredo Bruno +7 more
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Influenza vaccine effectiveness from nine studies during drifted A(H3N2) subclade K predominance, Europe, September 2025 to January 2026 [PDF]
EurosurveillanceThe European 2025/26 influenza season is dominated by the influenza A(H3N2) virus, with most sequenced viruses belonging to subclade K, genetically drifted from the vaccine virus, raising concerns around vaccine effectiveness (VE).
the European IVE group
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Early influenza virus characterisation and vaccine effectiveness in England in autumn 2025, a period dominated by influenza A(H3N2) subclade K [PDF]
EurosurveillanceInfluenza A(H3N2) subclade K (J.2.4.1) has dominated the 2025/26 season start in England. Post-infection ferret antisera raised against northern hemisphere 2025/26 vaccine strains showed reduced reactivity to subclade K viruses in England, aligning with ...
Jamie Lopez Bernal
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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
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Eurosurveillance[This article was retracted on 19 February 2026.]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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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) 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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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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