California has confirmed at least 52 measles cases so far in 2026, more than double last year's total, and San Mateo County remains among the eight counties with confirmed infections as local schools prepare to reopen Tuesday, Aug. 11.
The California Department of Public Health reported the figures as of July 20, putting the state on track for its highest annual measles total since 2015. Nationally, the outbreak is the worst in 35 years, with 2,318 confirmed cases already surpassing all of 2025, according to Patch.
As we reported July 22, San Mateo County had logged two confirmed cases earlier this year. The county is now listed alongside Napa, Orange, Placer, Riverside, Sacramento, San Francisco, and Shasta counties as areas with confirmed 2026 infections. The exact current San Mateo County case count has not been publicly updated.
The numbers are especially relevant for local families: both the San Mateo Union High School District and the San Mateo-Foster City School District begin classes Tuesday, Aug. 11, according to published school calendars.
Who's getting sick
About 52 percent of California's confirmed cases this year were children and young adults ages 5 to 19. Four people have been hospitalized.
No deaths have been reported.
State health officials said 94 percent of cases involved people who were unvaccinated or had an unknown vaccination status. The national figure is similar: 93 percent of U.S. cases are among unvaccinated individuals, according to the CDC.
"It is very concerning to see measles cases at their highest rate in 35 years, with numbers of cases in 2026 now exceeding those reported in 2025," said Dr. Monica Gandhi, an infectious disease expert at the University of California, San Francisco. "The increase in cases among children and young adults in California is also very worrisome and reflects declining vaccination rates among children."
What parents should do before Aug. 11
California law requires most school-age children to receive two doses of the measles, mumps, and rubella vaccine. Exemptions are allowed only for specific medical conditions under a 2015 state law. Two doses of the MMR vaccine are about 97 percent effective at preventing measles, according to the CDC.
Parents can verify their child's vaccination status through California's Digital Vaccine Record portal at myvaccinerecord.cdph.ca.gov, or by contacting their child's healthcare provider or previous school.
San Mateo County's first case this year involved an unvaccinated adult who had traveled internationally. County Health spokesperson Preston Merchant said in January, when that case was confirmed, that officials were working to reach anyone who may have been exposed.
Measles spreads through the air and via direct contact with infectious droplets. In a room with one infected person, nine out of 10 unvaccinated people will contract the disease, according to health officials. Symptoms including fever, cough, runny nose, pink eye, and a blotchy rash can appear between seven and 21 days after exposure.
Residents who believe they may have been exposed to measles should contact their healthcare provider or visit the San Mateo County Health website.
