Subclade K: The Superflu Surge of the 2025-2026 Season

The 2025-2026 flu season, driven by the highly infectious subclade K of the H3N2 virus, has resulted in record-high case numbers in the U.S. and Canada. Young children are severely affected, with high hospitalization rates. The CDC urges vaccination despite imperfect strain match in this season's vaccine.

A new flu variant, subclade K, is causing record high infection rates across the U.S. and Canada this season. With 91.5% of cases attributed to this subtype, the virus is proving especially dangerous for young children. Experts point to low population immunity as a potential reason for the outbreak.

Health officials report an alarming 15 million illnesses, with hospitals inundated by severe pediatric cases. Unlike previous seasons, when flu coincided with RSV or COVID-19, this year's influenza is creating its own massive impact. The spike is highlighted by unprecedented weekly doctor visits and emergency room admissions.

The CDC recommends prompt flu vaccination, although the current vaccine is not perfectly matched to subclade K. The shot can still mitigate illness severity. Experts stress adhering to health precautions, like frequent handwashing and staying home when sick, especially with the heightened contagiousness of subclade K.

(With inputs from agencies.)