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Dangerous New Flu Strain Hits US Weeks Early
16 Dec, 2025
Summary
- A new H3N2 subclade K flu strain is driving early, unexpected surges.
- Schools and hospitals are reinstating masking and restricting visitors.
- Nationwide flu test positivity increased to 8.1% in the week of Dec 6.
A dangerous new strain of the flu, identified as H3N2 subclade K, is causing a significant and early surge in cases across the United States. This "super flu" has appeared weeks ahead of the typical holiday spikes, prompting health officials to issue warnings and recommendations. The strain is proving particularly potent as it is new to many people's immune systems.
This widespread outbreak has already impacted public spaces, with schools like Poly Prep Country Day School in Brooklyn and Villa Duchesne Catholic School in St. Louis forced to close. Hospitals and health systems, including Hackensack Meridian Health and Detroit Medical Center, have reinstated masking protocols and visitor restrictions to combat the virus's rapid spread.
Data from December 6 shows "very high" transmission in New York City and "high" activity in states like New Jersey, Colorado, and Louisiana. Nationwide, 8.1% of flu tests were positive, with hospitalizations rising significantly compared to last year. Health officials are strongly advising flu vaccinations and vigilance for typical flu symptoms.
