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Abstract

We assessed haemagglutination inhibition (HAI) antibody titres against 2025 influenza A(H3N2) J.2 vaccine reference viruses and the novel subclade K (J.2.4.1) in age-stratified Hong Kong sera (collected May–July 2025), vaccine recipients and sera from virologically confirmed subclade J.2.2 or K infections. In contrast to mono-specific ferret sera, human sera with high J.2 HAI titres cross-reacted strongly with subclade K. Recombinant haemagglutinin- or egg-based standard dose J.2 A(H3N2) vaccines boosted geometric mean titres to K virus 5.6-fold and 2.6-fold, respectively.

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/content/10.2807/1560-7917.ES.2026.31.10.2600185
2026-03-12
2026-04-13
/content/10.2807/1560-7917.ES.2026.31.10.2600185
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Population immunity, post-vaccine and post-infection antibody responses to influenza A (H3N2) subclade J.2 and K (J.2.4.1) viruses, Hong Kong, 2025
<p class="citation"> <span>Citation style for this article:</span> <span class="meta-value authors"> <a href="/search?value1=Samuel+MS+Cheng&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Cheng Samuel MS</a>, <a href="/search?value1=Nancy+HL+Leung&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Leung Nancy HL</a>, <a href="/search?value1=Eunice+Y+Shiu&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Shiu Eunice Y</a>, <a href="/search?value1=Ricky+WK+Wong&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Wong Ricky WK</a>, <a href="/search?value1=Niki+YM+Au&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Au Niki YM</a>, <a href="/search?value1=Xiaotong+Huang&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Huang Xiaotong</a>, <a href="/search?value1=Natalie+KM+Kwok&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Kwok Natalie KM</a>, <a href="/search?value1=Coco+HC+Chan&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Chan Coco HC</a>, <a href="/search?value1=John+KC+Li&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Li John KC</a>, <a href="/search?value1=Leo+CH+Tsang&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Tsang Leo CH</a>, <a href="/search?value1=Tsz+Chun+Kwan&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Kwan Tsz Chun</a>, <a href="/search?value1=Tim+K+Tsang&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Tsang Tim K</a>, <a href="/search?value1=Leo+LM+Poon&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Poon Leo LM</a>, <a href="/search?value1=Benjamin+J+Cowling&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Cowling Benjamin J</a>, <a href="/search?value1=Malik+Peiris&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Peiris Malik</a></span>. Population immunity, post-vaccine and post-infection antibody responses to influenza A (H3N2) subclade J.2 and K (J.2.4.1) viruses, Hong Kong, 2025. <a href="/content/ecdc">Euro Surveill.</a> 2026;31(10):pii=2600185. <a href="https://doi.org/10.2807/1560-7917.ES.2026.31.10.2600185" title="doi link" target="_blank">https://doi.org/10.2807/1560-7917.ES.2026.31.10.2600185</a> <span class="ES_Article_citation"> <span class="generated">Received</span>: 02 Mar 2026;&nbsp;&nbsp; <span class="generated">Accepted</span>: 11 Mar 2026 </span> </p>
/content/10.2807/1560-7917.ES.2026.31.10.2600185
/content/10.2807/1560-7917.ES.2026.31.10.2600185
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