California by 2026 has already seen the highest number of annual measles cases in seven years, health officials said, amid a resurgence of the most popular contagious disease once considered successfully eradicated in the United States.
The new outbreak of the disease comes as vaccination rates have fallen across the country in recent years – in some areas falling below the herd vaccination threshold that is required to prevent the spread.
“There are pockets of vulnerability, such as in communities, which can lead to outbreaks of violence,” said Dr. Peter Chin-Hong, an infectious disease specialist at UC San Francisco.
So far this year, there have been at least 40 confirmed cases of measles in California. That is far more than the 25 recorded in the year 2025, according to Dr. Eric Sergienko, chief of infectious disease control at the Department of Public Health. And it’s already the state’s highest single-year total since 2019, when there were 73.
The latest case of measles was announced Wednesday: an infant from San Francisco who was too young to be vaccinated and picked up the virus on international travel. It was the first measles case in San Francisco since 2019. (The baby’s family was all vaccinated.)
The spread of the highly contagious virus occurs mostly among unvaccinated people, especially children and young adults, provincial health data show. Of the first 39 measles cases reported this year in California, 95% were among people who were unvaccinated or had unknown vaccination status, and 85% were among people under the age of 20, Sergienko said at a health conference this week.
The measles vaccine – commonly called MMR, as it also confers protection against two other once common childhood diseases, measles and rubella – is considered 97% effective in preventing illness after receiving two recommended doses, and 93% effective after one shot. Vaccinated people are less likely to get mumps, although they tend to have a mild illness, according to the US Centers for Disease Control and Prevention.
It was a generation ago, in 2000, that the US declared the ongoing spread of measles to be over – a public health success attributed to a strong vaccination effort following the outbreak of the disease from 1989 to 1991.
But some experts now fear that the US is in danger of allowing the virus to gain momentum again. Nationwide, there have been at least 1,714 confirmed cases of measles so far this year, approaching a total of 2,287 by 2025, according to the CDC.
The number of cases recorded in 2025 was the highest in one year since 1991. Most of them, 90%, were linked to outbreaks.
For every 10,000 people infected with measles, 500 children are statistically at risk of developing pneumonia, and 30 of them may die, Sergienko said.
There were three reported deaths from measles nationally last year – two among unvaccinated school children in Texas and one in an unvaccinated adult in New Mexico.
Los Angeles County in September reported the death of a school-aged child due to complications from measles. The child was infected as an infant when he was too young to be vaccinated, and years later developed subacute sclerosing panencephalitis, or SSPE, a fatal disease that attacks the brain.
Children usually receive their first dose of MMR when they are 12 to 15 months old and the second when they are 4 to 6 years old, according to the CDC.
Children ages 6 to 11 months and traveling internationally should receive a dose, but should still receive a series of two regular doses after their first birthday, the CDC says.
There have been three outbreaks fueling the spread of measles in California so far this year: one in Riverside County, involving three people infected with the virus in one family; one in Shasta County, infected nine people in a church group; and ongoing violence in Sacramento County and neighboring Placer County, Sergienko said.
The Sacramento Valley outbreak was first identified in February, when officials reported that an unvaccinated child contracted measles after returning from South Carolina — where an outbreak centered in Spartanburg County has been linked to nearly 1,000 cases, health officials said. It is considered one of the biggest epidemics in the US in more than 30 years.
Measles was then found in three siblings from another home in Placer County who were in contact with the infant.
Then in early March, another case of measles was found in a child from the same community who attended what authorities described as an educational enrichment program, potentially exposing up to 130 children to the virus, California health officials said. The organizers of this educational program agreed to close their center temporarily.
LA County has reported four cases of measles this year so far — all among those who have recently traveled abroad. The latest case involved someone aboard a Singapore Airlines flight that arrived at Los Angeles International Airport on Feb. 9.
Orange County has reported a case of measles in a young adult who may have been exposed to people at a gym and an urgent care center in Ladera Ranch, as well as a case in a young child. They also reported two cases of measles among travelers to Disneyland, one on Jan. 22 and another on Jan. 28.
San Bernardino County reported a case of measles in an unvaccinated child who traveled from another county. San Diego County said an unvaccinated traveler living outside the county could have exposed people while visiting the emergency room at a local hospital in mid-March.
In the Bay Area, health officials reported a case of measles in a vaccinated Santa Clara County resident who recently returned from an international trip, and who may have exposed people to a restaurant in Burlingame on Feb. 23 and Feb. 24.
Measles is one of the most contagious viruses known to man. It can be spread by coughing and sneezing, and remains airborne for up to two hours after an infected person has left the room. If infected, a person will begin to show symptoms of measles seven to 21 days after exposure.
Officials expect the measles outbreak in the Sacramento Valley to continue for at least the next few weeks.
“Since four cases have just appeared in the last week, we expect that this outbreak will continue for at least another incubation period, 21 days or more, as we look at possible undocumented infections in the affected community,” Sergienko said on Tuesday.
Nationally, measles vaccination rates among preschool children have been declining. In the 2019-20 school year, 95.2% of 95.2-year-olds were fully vaccinated, but that dropped to 92.5% in the 2024-25 school year — below the herd immunization target of 95%, according to the CDC.
The measles vaccination rate for California preschoolers was 96.1% in 2024-25, among the highest in the nation. Some of the states that experienced the biggest boom had preschool enrollment rates below the 95% goal – Texas was 93.2%; New Mexico, 94.8%; and South Carolina, 91.2%.
California has sweeping immunization requirements as a condition of enrollment in public and private schools, and child care centers, except for medical reasons. Parents who choose not to vaccinate because of their beliefs can homeschool their children and enroll them in private tutoring, as long as they are “not receiving classroom-based education.”
But, as a Times story last year noted, California laws don’t define what “classroom-based instruction” means, including whether students need to be vaccinated if they attend certain in-person classes or school-sanctioned activities like field trips, football practices or prom. Opponents of school immunization requirements are also working to pressure states like California to weaken them.
Anti-vaccination advocates have been emboldened in recent years by the rise of Health and Human Services Secretary Robert F. Kennedy Jr., a longtime vaccine skeptic.
March 2025, Kennedy issued a statement which noted the effectiveness of vaccines in preventing the spread of measles, but stopped short of specifically recommending that parents vaccinate their children.
But as the year progressed, Kennedy and the agencies he led promoted a national vaccine delivery program, while publicly sharing misleading and inaccurate information about vaccination.
As recent outbreaks show, measles can spread quickly if it enters pockets of unvaccinated communities, and children too young to be vaccinated can be at risk of serious illness and death.
One such example was the measles outbreak at Disneyland from December 2014 to April 2015, which resulted in 131 cases in California, and spread to people in six other states, as well as Canada and Mexico. Among people with measles in California, at least 12 of those who contracted the disease were children too young to be vaccinated.
Measles symptoms rarely start with an outbreak, Sergienko said. The disease begins with a mild to moderate fever, followed by a cough, runny nose and red, watery eyes. It takes two or three days later before small white sores, known as Koplik’s spots, appear on the inside of the mouth, and more fever may develop, with temperatures exceeding 104 degrees.
A few days later, a red rash appeared, starting on the hairline and working its way down, Sergienko said.
Officials urge people who suspect that they or their child has measles to call the health department. Healthcare providers are advised to test a patient suspected of having measles in a way that will not expose other patients to the virus.
Health officials have urged people to step up with the measles vaccine if they have not already done so.
“We all need to work together to share the medical evidence, benefits, and safety of vaccines to give families the information they need to protect our children and communities,” said Dr. Erica Pan, director of the California Department of Public Health.
