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2w ago

Drifted H3N2 ‘Subclade K’ Drives Early U.S. Flu Uptick Before Holidays

Health agencies say the current vaccine still reduces severe outcomes despite a partial mismatch.

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FILE - A patient is given a flu vaccine Oct. 28, 2022, in Lynwood, Calif. On Tuesday, July 2, 2024, the U.S. (AP Photo/Mark J. Terrill, File)
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Signage for flu shots outside a Walmart store in Martinez, Calif., on Nov. 20, 2025.

Overview

  • CDC data through the week ending Nov. 15 show 115 of 160 recent influenza A detections (about 72%) were H3N2 as overall flu activity increases.
  • The CDC estimates at least 650,000 illnesses, 7,400 hospitalizations, and 300 deaths so far this season.
  • Preliminary UK analyses indicate this season’s vaccine is roughly 70–75% effective at preventing hospitalization in children and about 30–40% in adults.
  • Clinicians report earlier-than-usual case growth, with H3N2 historically linked to more severe outcomes in older adults and young children.
  • CDC reporting was paused Sept. 20–Nov. 8 during the government shutdown, and officials are urging vaccination, early antiviral treatment, and basic precautions as they monitor trends.