Science Friday How A Mutation Made This Year’s Flu Season So Bad
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Jan 26, 2026 Jennifer Duchon, a pediatric infectious disease specialist at Mount Sinai, breaks down why this season’s H3N2 subclade K surged and why the flu shot was a poor match. She discusses how H3N2 drifts, prospects for better and universal vaccines, CDC policy effects on children, and antiviral timing and personal precautions.
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Antigenic Drift Caused The Mismatch
- An H3N2 subclade called K developed antigenic mutations that reduced vaccine match.
- That drift explains why vaccinated people still got sick this season.
Still Get Vaccinated This Season
- Get the flu vaccine because it still reduces severe outcomes like hospitalization.
- Vaccination offers partial protection even when strains drift antigenically.
K Is A Drift, Not A New Pandemic Strain
- The K subclade is a small branching change within H3N2, not a completely new strain.
- This represents antigenic drift rather than the 2009-like novel strain emergence.