Eurosurv. Interim 2025/26 influenza vaccine effectiveness estimates with immuno-epidemiological considerations for A(H3N2) subclade K protection, Cana

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• Lea Separovic[SUP]1[/SUP] , Suzana Sabaiduc[SUP]1[/SUP] , Yuping Zhan[SUP]1[/SUP] , Samantha E Kaweski[SUP]1[/SUP] , Romy Olsha[SUP]2[/SUP] , Maan Hasso[SUP]2[/SUP] , Richard G Mather[SUP]2,3[/SUP] , Sara Carazo[SUP]4[/SUP] , Christine Lacroix[SUP]4[/SUP] , Isabelle Meunier[SUP]4[/SUP] , Lila N Salhi[SUP]4[/SUP] , James A Dickinson[SUP]5[/SUP] , Nathan Zelyas[SUP]6[/SUP] , Agatha N Jassem[SUP]1[/SUP] , Katie Dover[SUP]1[/SUP] , Charlene Ranadheera[SUP]7[/SUP] , Ruimin Gao[SUP]7[/SUP] , Nathalie Bastien[SUP]7[/SUP] , Danuta M Skowronski[SUP]1,8[/SUP]

​In 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 distinct subclade K, by about 40% relative to unvaccinated individuals. Vaccine effectiveness was about 30% against A(H1N1)pdm09, with insufficient case numbers for interim influenza B estimation. Meaningful protection against subclade K, despite substantial vaccine mismatch, is interpreted in the context of immuno-epidemiological considerations, including potential viral glycosylation, imprinting, and pre-immunity effects.

https://www.eurosurveillance.org/content/10.2807/1560-7917.ES.2026.31.5.2600068