Eurosurv. Early influenza virus characterisation and vaccine effectiveness in England in autumn 2025, a period dominated by influenza A(H3N2) subc

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• Freja CM Kirsebom[SUP]1[/SUP] , Catherine Thompson[SUP]2[/SUP] , Tiina Talts[SUP]2[/SUP] , Beatrix Kele[SUP]2[/SUP] , Heather J Whitaker[SUP]3[/SUP] , Nick Andrews[SUP]1[/SUP] , Nurin Abdul Aziz[SUP]1[/SUP] , Christopher Rawlinson[SUP]1[/SUP] , Rebecca E Green[SUP]1[/SUP] , Catherine Quinot[SUP]1[/SUP] , Nicholas Gardner[SUP]1[/SUP] , Elizabeth Waller[SUP]1[/SUP] , Alex Allen[SUP]1[/SUP] , Conall H Watson[SUP]1,4[/SUP] , Suzanna LR McDonald[SUP]1[/SUP] , Maria Zambon[SUP]2[/SUP] , Richard Pebody[SUP]4,5[/SUP] , Mary Ramsay[SUP]6,7[/SUP] , Katja Hoschler[SUP]2[/SUP] , Anika Singanayagam[SUP]2,4,*[/SUP] , Jamie Lopez Bernal[SUP]1,4,*[/SUP]

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Influenza 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 World Health Organization reports. Nevertheless, early post-vaccination, vaccine effectiveness against influenza-related emergency department attendances and hospital admissions remained within typical ranges, at 72–75% in children and adolescents (< 18 years) and 32–39% in adults. Hence, vaccination remains effective against clinical disease caused by influenza A(H3N2) viruses.

https://www.eurosurveillance.org/content/10.2807/1560-7917.ES.2025.30.46.2500854#html_fulltext