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Friday, Dec. 12, 2025

Did the flu variant H3N2/K emerge before this year’s vaccine was formulated?

Mariana Navarrete Villegas, CT Mirror
no

A new influenza A(H3N2) virus strain renamed “H3N2 subclade K,” which is circulating widely today, was identified by health organizations months after the seasonal influenza vaccine was developed.

The World Health Organization selected the components for the northern hemisphere influenza vaccine between February and March of this year. Since August, there has been a rapid increase of A(H3N2) subclade K.

The Centers for Disease Control and Prevention explains that even if the current vaccine does not match the flu virus mutation that is currently being spread — the “K” variant — vaccination continues to protect against severe illness, hospitalization and death, as well as offering protection against other influenza viruses and help reduce the overall community spread.

Connecticut Public Health confirmed a Hartford County resident died from influenza the week of Oct. 25.

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