The ‘Super Flu’ Spreading in the United States and Europe

The spread of influenza became more severe this fall, particularly in the United States and the United Kingdom. The U.S. Centers for Disease Control and Prevention (CDC) has designated the 2024-25 flu season as the most severe season since 2017-18. In the U.K., the spread has begun earlier than at any time since 2003-04.

Against this backdrop, some media outlets have begun using the term "super flu." However, this term is not an official medical term. The actual name is "subclade K," a new variant of influenza A H3N2.

This variant has multiple mutations in a protein on the surface of the virus called hemagglutinin, making it antigenically different from the variants used in existing vaccines. This allows it to partially evade immunity acquired through previous infection or vaccines, making people more susceptible to infection. Genetic analysis by the UK Health Security Agency has revealed that 87 percent of H3N2 viruses detected since late August 2025 are subclade K.

Please select this link to read the complete article from WIRED.