California sees the most measles cases in 7 years as disease resurges nationwide

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California in 2026 has already seen its highest number of annual measles cases in seven years, health officials said, amid an ongoing resurgence of a notoriously infectious disease once considered effectively eliminated in the United States.The looming new domestic beachhead for the disease comes as vaccination rates have tumbled nationwide in recent years — in some areas falling well below the herd immunity threshold experts say is necessary to keep it from spreading.“There are pockets of vulnerability, like in communities, that can really lead to outbreaks going wild,” said Dr.Peter Chin-Hong, a UC San Francisco infectious diseases expert.

So far this year, there have been at least 40 confirmed measles cases in California.That’s well above the 25 recorded in all of 2025, according to Dr.

Eric Sergienko, chief of the state Department of Public Health’s communicable disease control division.It’s also already the state’s highest single-year tally since 2019, when there were 73.The latest measles case was announced Wednesday: an infant from San Francisco who was too young to be vaccinated and picked up the virus during an international trip.

It was San Francisco’s first measles case since 2019.(The infant’s family was all vaccinated.) California Measles has been a scourge for centuries, afflicting millions of people.

The spread of the highly infectious virus is largely occurring among unvaccinated individuals, particularly children and younger adults, state health data show.Of the first 39 measles cases reported this year in California, 95% were among people who were unvaccinated or had an unknown immunization status, and 85% were in individuals under age 20, Sergienko said in a briefing to health professionals this week.The measles vaccine — usually referred to as MMR, as it also conveys protection against two other once-common childhood illnesses, mumps an...