In 2025, the US surpassed its highest annual case count of measles in more than 30 years, mostly in unvaccinated children. An immunization rate of at least 95% is necessary for herd immunity to measles. Study identified 8 counties in California with census tracts with less than 95% coverage.

In 2025, the US surpassed its highest annual case count of measles in more than 30 years, mostly in unvaccinated children. An immunization rate of at least 95% is necessary for herd immunity to measles. Study identified 8 counties in California with census tracts with less than 95% coverage.