Flu season is worse as H3N2 subclade K makes vaccines somewhat less effective

Officials report a worse-than-usual flu season linked to an H3N2 subgroup called subclade K, and about 44 percent of U.S. adults have received the flu vaccine so far.

Health reports describe a worse-than-usual flu season linked to a subgroup of the H3N2 virus called subclade K. Experts say that subclade carries multiple mutations that have reduced the match with this season's vaccine, though the vaccine is not described as completely ineffective. Vaccination coverage is lower than before the Covid pandemic, with around 44 percent of U.S. adults vaccinated so far. The decline in uptake has been especially marked for children, and pediatric hospitalizations are higher than normal. Key points: - The season involves H3N2 subclade K, which is reported to carry mutations that lessen the vaccine match. - The current vaccine is reported as not completely ineffective, but its effectiveness appears reduced against this subgroup. - About 44 percent of U.S. adults have had the flu vaccine so far, a decline from pre-pandemic levels. - Declines in child vaccination coincide with higher-than-normal pediatric hospitalizations. Summary: The reported combination of an evolving H3N2 subclade and lower vaccination rates coincides with a more severe season and increased pediatric hospitalizations. Undetermined at this time.