Flu season is worse now as subclade K spreads across the U.S.

A new H3N2 subclade K variant is driving a sharp rise in flu cases and hospitalizations across the U.S., and the CDC reports high activity in 32 states as this season's vaccine is reported to be less well matched to the circulating strain.

We are entering peak flu season and public health officials report a rapid rise in cases linked to a new H3N2 subclade K virus. The variant has mutations that differ from strains that circulated last year and from the vaccine strain chosen earlier. Health authorities say hospitalizations are increasing across many parts of the country and that the current wave may continue for weeks. Key facts: - Officials report the spread of a subclade K H3N2 virus that has changes at immune-targeted sites compared with last season's viruses. - The CDC reported flu activity as high or very high in 32 states and jurisdictions, and national counts cited millions of infections and thousands of deaths so far this season. - Public reporting indicates the vaccine strain selected earlier this year is a partial mismatch to the circulating clade K virus, which is expected to reduce vaccine effectiveness against infection while some protection against severe disease may remain. - Health officials have said the current wave could last for weeks as the variant moves through different parts of the country. Summary: The emergence of subclade K has increased susceptibility in the population because it differs from recent circulating viruses and from the vaccine strain chosen months earlier. As a result, flu activity and hospitalizations have risen across many states, and public health authorities expect this wave to continue for several weeks.