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Abstract

The 2025/26 season was marked by co-circulation of influenza A subtypes, with the first detection of A(H3N2) subclade K in September 2025. In August 2025 in Portugal, 14.8% (95% CI: 12.2–17.8) of 886 persons tested had cross-protective antibodies against this subclade. The overall seroprevalence against circulating A(H1N1)pdm09 strains was 28.1% (95% CI: 24.4–32.0). These data highlight the presence of previous cross-reactive antibodies and the possible advantage of vaccination in the extent of detectable antibodies against influenza viruses.

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/content/10.2807/1560-7917.ES.2026.31.6.2600070
2026-02-12
2026-03-15
/content/10.2807/1560-7917.ES.2026.31.6.2600070
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Cross-sectional study on protective antibodies against influenza A virus subtypes and cross-protection against influenza A(H3N2) subclade K, Portugal, August 2025
<p class="citation"> <span>Citation style for this article:</span> <span class="meta-value authors"> <a href="/search?value1=Raquel+Guiomar&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Guiomar Raquel</a>, <a href="/search?value1=Camila+Henriques&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Henriques Camila</a>, <a href="/search?value1=Susana+Pereira+da+Silva&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Pereira da Silva Susana</a>, <a href="/search?value1=Lic%C3%ADnia+Gomes&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Gomes Licínia</a>, <a href="/search?value1=Daniela+Dias&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Dias Daniela</a>, <a href="/search?value1=Nuno+Verdasca&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Verdasca Nuno</a>, <a href="/search?value1=Portuguese+Laboratory+Network+for+the+Diagnosis+of+Influenza+and+Respiratory+Viruses&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Portuguese Laboratory Network for the Diagnosis of Influenza and Respiratory Viruses</a>, <a href="/search?value1=Baltazar+Nunes&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Nunes Baltazar</a>, <a href="/search?value1=Ana+Paula+Rodrigues&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Rodrigues Ana Paula</a></span>. Cross-sectional study on protective antibodies against influenza A virus subtypes and cross-protection against influenza A(H3N2) subclade K, Portugal, August 2025. <a href="/content/ecdc">Euro Surveill.</a> 2026;31(6):pii=2600070. <a href="https://doi.org/10.2807/1560-7917.ES.2026.31.6.2600070" title="doi link" target="_blank">https://doi.org/10.2807/1560-7917.ES.2026.31.6.2600070</a> <span class="ES_Article_citation"> <span class="generated">Received</span>: 29 Jan 2026;&nbsp;&nbsp; <span class="generated">Accepted</span>: 11 Feb 2026 </span> </p>
/content/10.2807/1560-7917.ES.2026.31.6.2600070
/content/10.2807/1560-7917.ES.2026.31.6.2600070
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