Eurosurv. Influenza vaccine effectiveness from nine studies during drifted A(H3N2) subclade K predominance, Europe, September 2025 to January 2026

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• Heloise Lucaccioni[SUP]1,*[/SUP] , Diogo FP Marques[SUP]1,*[/SUP] , Freja Kirsebom[SUP]2[/SUP] , Hanne-Dorthe Emborg[SUP]3[/SUP] , Mark Hamilton[SUP]4[/SUP] , Heather Whitaker[SUP]2[/SUP] , Amanda Bolt Botnen[SUP]5[/SUP] , Magda Bucholc[SUP]6[/SUP] , Francisco Pozo[SUP]7,8[/SUP] , Nick Andrews[SUP]2[/SUP] , Ramona Trebbien[SUP]5[/SUP] , Safraj Shahul Hameed[SUP]4[/SUP] , Karina Lauenborg Møller[SUP]9[/SUP] , Mark G O’Doherty[SUP]6[/SUP] , Jamie Lopez-Bernal[SUP]2[/SUP] , Kirsty Morrison[SUP]4[/SUP] , Simon Cottrell[SUP]10[/SUP] , Suzanne Wilton[SUP]6[/SUP] , Angela MC Rose[SUP]1,**[/SUP] , Esther Kissling[SUP]1,**[/SUP] , the European IVE group[SUP]11[/SUP]

The 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). Despite this, VE estimates from nine European studies (19 countries) indicate all-age influenza A VE of 25–45% for outpatient and hospital settings combined, similar to other seasons, with highest estimates among children (47–72%). Vaccination should be encouraged and complemented by other infection prevention and control measures.

https://www.eurosurveillance.org/content/10.2807/1560-7917.ES.2026.31.7.2600109
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