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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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2026-02-05
2026-02-08
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Interim 2025/26 influenza vaccine effectiveness estimates with immuno-epidemiological considerations for A(H3N2) subclade K protection, Canada, January 2026
<p class="citation"> <span>Citation style for this article:</span> <span class="meta-value authors"> <a href="/search?value1=Lea+Separovic&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Separovic Lea</a>, <a href="/search?value1=Suzana+Sabaiduc&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Sabaiduc Suzana</a>, <a href="/search?value1=Yuping+Zhan&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Zhan Yuping</a>, <a href="/search?value1=Samantha+E+Kaweski&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Kaweski Samantha E</a>, <a href="/search?value1=Romy+Olsha&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Olsha Romy</a>, <a href="/search?value1=Maan+Hasso&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Hasso Maan</a>, <a href="/search?value1=Richard+G+Mather&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Mather Richard G</a>, <a href="/search?value1=Sara+Carazo&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Carazo Sara</a>, <a href="/search?value1=Christine+Lacroix&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Lacroix Christine</a>, <a href="/search?value1=Isabelle+Meunier&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Meunier Isabelle</a>, <a href="/search?value1=Lila+N+Salhi&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Salhi Lila N</a>, <a href="/search?value1=James+A+Dickinson&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Dickinson James A</a>, <a href="/search?value1=Nathan+Zelyas&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Zelyas Nathan</a>, <a href="/search?value1=Agatha+N+Jassem&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Jassem Agatha N</a>, <a href="/search?value1=Katie+Dover&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Dover Katie</a>, <a href="/search?value1=Charlene+Ranadheera&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Ranadheera Charlene</a>, <a href="/search?value1=Ruimin+Gao&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Gao Ruimin</a>, <a href="/search?value1=Nathalie+Bastien&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Bastien Nathalie</a>, <a href="/search?value1=Danuta+M+Skowronski&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Skowronski Danuta M</a></span>. Interim 2025/26 influenza vaccine effectiveness estimates with immuno-epidemiological considerations for A(H3N2) subclade K protection, Canada, January 2026. <a href="/content/ecdc">Euro Surveill.</a> 2026;31(5):pii=2600068. <a href="https://doi.org/10.2807/1560-7917.ES.2026.31.5.2600068" title="doi link" target="_blank">https://doi.org/10.2807/1560-7917.ES.2026.31.5.2600068</a> <span class="ES_Article_citation"> <span class="generated">Received</span>: 30 Jan 2026;&nbsp;&nbsp; <span class="generated">Accepted</span>: 05 Feb 2026 </span> </p>
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