What question did this study set out to answer?

This research aims to estimate the effectiveness of the influenza vaccine against the A(H3N2) subclade K and other strains in Canada.

February 8, 2026Open Access

Interim 2025/26 influenza vaccine effectiveness estimates with immuno-epidemiological considerations for A(H3N2) subclade K protection, Canada, January 2026

Key Points

This research aims to estimate the effectiveness of the influenza vaccine against the A(H3N2) subclade K and other strains in Canada.
Utilized data from the Canadian Sentinel Practitioner Surveillance Network
Analyzed medically-attended acute respiratory illness cases
Estimated vaccine effectiveness for A(H3N2) and A(H1N1)pdm09
Influenza vaccine reduced acute illness risk by about 40% against A(H3N2) subclade K
Vaccine effectiveness was approximately 30% against A(H1N1)pdm09
Insufficient data was available for interim estimation of influenza B effectiveness

Abstract

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.

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Cite This Study

Separovic et al. (Thu,) studied this question.

synapsesocial.com/papers/698827e20fc35cd7a8846dc8 https://doi.org/https://doi.org/10.2807/1560-7917.es.2026.31.5.2600068

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