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Flu Surges to 25-Year High as H3N2 ‘Subclade K’ Drives U.S. Wave

Early evidence suggests this season’s vaccine still offers meaningful protection against the drifted strain.

Overview

  • CDC data show doctors’ visits for flu-like illness at their highest levels since the late 1990s, with an estimated 11 million illnesses, 120,000 hospitalizations and 5,000 deaths so far this season.
  • Roughly 90% of H3N2 samples further characterized are the subclade K variant, and most states report high or very high activity with Florida among the hardest hit.
  • Ohio recorded 1,465 flu-related hospitalizations for the week ending Jan. 3, exceeding last year’s comparable week, while New York City saw a slight local dip and Illinois flagged very high activity and rising pediatric impact.
  • Health authorities report no evidence that subclade K causes more severe disease than prior H3N2 strains, though its genetic drift has helped it spread widely in more than 30 countries.
  • Researchers reported the current shot boosted measurable antibodies against subclade K in a new preprint, and clinicians continue to urge vaccination, early antiviral treatment, and standard prevention steps.