Eurosurv. Interim estimates of vaccine effectiveness against influenza A(H1N1)pdm09 and A(H3N2) during a delayed influenza season, Canada, 2024/25

[tetano]

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

The Canadian Sentinel Practitioner Surveillance Network (SPSN) reports interim 2024/25 vaccine effectiveness (VE) against acute respiratory illness due to laboratory-confirmed influenza during a delayed season of predominant A(H1N1)pdm09 and lower A(H3N2) co-circulation. Through mid-January, the risk of outpatient illness due to influenza A is reduced by about half among vaccinated vs unvaccinated individuals. Adjusted VE is 53% (95% CI: 36–65) against A(H1N1)pdm09, comprised of clades 5a.2a and 5a.2a.1, and 54% (95% CI: 29–70) against A(H3N2), virtually all clade 2a.3a.1.
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https://www.eurosurveillance.org/content/10.2807/1560-7917.ES.2025.30.4.2500059