Eurosurv. Extended influenza seasons in Australia and New Zealand in 2025 due to the emergence of influenza A(H3N2) subclade K viruses

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• Clyde Dapat[SUP]1,*[/SUP] , Heidi Peck[SUP]1,*[/SUP] , Lauren Jelley[SUP]2[/SUP] , Tanya Diefenbach-Elstob[SUP]1[/SUP] , Tegan Slater[SUP]2[/SUP] , Saira Hussain[SUP]1[/SUP] , Phillip Britton[SUP]3,4[/SUP] , Allen C. Cheng[SUP]5[/SUP] , Tim Wood[SUP]2[/SUP] , Annaleise Howard-Jones[SUP]3,4[/SUP] , Yi Mo Deng[SUP]1[/SUP] , Jessica E. Miller[SUP]1[/SUP] , Q. Sue Huang[SUP]2[/SUP] , Ian G. Barr[SUP]1,6[/SUP]
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In Australia and New Zealand, late outbreaks of an A(H3N2) variant virus termed subclade K extended the 2025 influenza season. Subclade K viruses were genetically and antigenically distinct from the 2025 vaccine A(H3N2) strain A/Croatia/10136RV/2023 (H3N2)-like virus and previously circulating subclade J viruses. Subclade K viruses have since been detected in over 34 countries and appear to have spread globally, except in South America. It is thus likely that they will further expand during the northern hemisphere winter 2025/26 season.

​https://www.eurosurveillance.org/content/10.2807/1560-7917.ES.2025.30.49.2500894