21 hours ago · A newly mutated H3N2 subclade K flu strain with seven mutations is spreading fast worldwide, causing rising cases and concerns over vaccine mismatch.

A mutated flu virus is spreading across the U.S., with 86.8% of recent cases identified as H3N2 subclade K. The flu shot is estimated to be effective against it.

Dec 4, 2025 · Infectious diseases reporter Helen Branswell discusses this year's vaccine and the new flu strain that's circulating, H3N2 subclade K.

16 hours ago · What is the H3N2 flu strain? Symptoms and advice as UK cases surge Health bosses are warning this winter could see the ‘most severe flu outbreak in decades’

Dec 5, 2025 · The CDC reports the new H3N2 subclade K is particularly affecting younger populations as the country enters peak flu season between December and February.

Nov 30, 2025 · As we get deeper into flu season, a new type of the influenza virus has been identified, the Centers for Disease Control and Prevention confirms.

3 days ago · Published: 9 December 2025 A heavily mutated flu strain — A/H3N2 subclade K, often dubbed the “K-strain” or “superflu” — is now dominating the 2025–26 flu season and driving record …

2 days ago · Local health officials are alerting the public to a new strain of influenza A that has begun circulating this flu season.

3 days ago · With the spread of the new strain, and fewer people getting vaccinated, the flu season could be rough. While the new variant – which emerged too late for it to be incorporated into the …

Dec 1, 2025 · A new flu variant called subclade K is gaining attention as doctors warn it could lead to a tougher flu season this winter. The strain, which stems from the influenza A (H3N2) virus, has already ...