San Mateo County public health officials confirmed Thursday that a positive case of measles has been reported in the area — appearing to make it California’s first measles case of 2026.
The case was detected in an unvaccinated adult who had traveled outside the United States, according to San Mateo County Health spokesperson Preston Merchant.
“We are still working on reaching anyone who may have been exposed, but so far no one else has developed symptoms,” Merchant said.
In 2025, the county confirmed a previous measles case that also followed international travel, Merchant noted.
In its weekly report, the California Department of Public Health has recorded one measles case statewide in 2026. However, the agency has not yet confirmed to KQED whether that is the same as the San Mateo County case — or if more measles cases have been recorded since the report was published on Tuesday.
The Centers for Disease Control and Prevention’s own measles reporting indicates that three cases of the virus have been recorded nationwide since Jan. 1, but it said these cases were reported in North Carolina and South Carolina — indicating the California case has not yet been included.
California saw 25 cases of measles in 2025, according to NBC’s tracker using CDC data — contributing to a total of 2,144 confirmed cases nationwide.
Last year saw the country’s highest number of measles cases since the disease was eliminated in the year 2000, according to the CDC data.
Symptoms of measles — a highly contagious virus that spreads through direct contact with infectious droplets — include fever, cough, runny nose and pink eye, followed a few days later by a rash. These symptoms can emerge between seven and 21 days after exposure.
About 1 in 5 unvaccinated people who become infected with measles will require hospitalization, according to the CDC. In some people, the disease can be fatal.
The San Mateo County case this week comes on the heels of Contra Costa Health’s Dec. 29 announcement that a case of measles had been confirmed in that county, in an individual who had been contagious in public between Dec. 17 and Dec. 24.
According to CDC data from the 2023-24 school year, California has a 96.2% vaccination rate against measles.
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