Overview
- The World Health Organization says H3N2 subclade K is rapidly spreading and predominating in parts of the Northern Hemisphere, with early hospitalizations reported in the U.K. and Canada.
- The CDC reports U.S. influenza activity remains low but is increasing, with most detected viruses in the H3N2 A category and higher recent positivity and emergency visits among children.
- Experts caution the season’s H3N2 vaccine may not match subclade K well, yet preliminary U.K. data suggest the shot reduces hospitalizations by up to about 75% in children and up to about 40% in adults.
- The CDC’s Nov. 17 update recommends vaccination for everyone 6 months and older, noting the flu shot helps reduce the severity of illness even when the match is imperfect.
- U.S. flu vaccinations are lagging last year by roughly 2 million doses through October, and experts note limited domestic genomic data on subclade K circulation following recent government and staffing disruptions.