Despite having some of the nation’s strictest school vaccination laws, California reported a decline last year in the share of kindergarten students who were immunized against measles, including in 16 counties where students no longer have herd immunity against one of the most contagious diseases.
New data from the California Department of Public Health show that last year, 96.2% of California students in transitional kindergarten and kindergarten were vaccinated against measles, mumps and rubella in the 2023-24 school year, down from 96.5% the year before. And 93.7% of kindergarten students were up to date on all their immunizations, down from 94.1% in the same period the previous year. Data on vaccination rates for first-grade students, which are usually higher, were not yet available.
California’s childhood vaccination rates are still higher than in the U.S. overall. But public health experts say the declining immunization rate creates two main risks: that measles could spread here amid the deadly outbreak that began in Texas, and that the immunization rate could continue to fall.
The COVID-19 pandemic worsened trust in public health institutions, experts say, and there’s growing concern that deep political discord, along with widespread disinformation online, will only make it harder to reverse the downward trend.
A 95% vaccination rate, sometimes called “herd immunity,” is generally considered the gold standard of disease prevention. That threshold not only prevents infections from ripping through a community, but also protects those who are not able to get vaccinated because they are pregnant, immunocompromised or have other serious health issues.
“Measles is so infectious,” said Dr. Chad Vercio, division chief of general pediatrics at Loma Linda University Children’s Health in San Bernardino County, where about 93.5% of kindergarten students were immunized against measles last year.
When fewer people are vaccinated against the disease, he said, “the likelihood that someone who’s not been vaccinated gets infected becomes so much higher.”
Measles is most often associated with a high fever and rash, but more severe cases can cause pneumonia or encephalitis. The disease kills about one to three people for every 1,000 infected and leads to hospitalization in 1 in 5 cases, Vercio said.
California’s vaccine laws, which were tightened in the wake of the 2014-15 measles outbreak at Disneyland, make it difficult for parents to send children to school without a series of standard childhood vaccines, including the shots known as DTaP, short for diphtheria, tetanus, and pertussis; and MMR, short for measles, mumps and rubella.
Still, the state’s childhood immunization rates have been falling for the better part of a decade.
Vercio said he and other local pediatricians have seen a “significant” increase in vaccine hesitancy since the start of the pandemic, including parents who refuse to discuss immunizations with their doctors after encountering misinformation online about vaccines, including the debunked connection between vaccines and autism.
Last year, nearly two-thirds of California’s counties reported immunization rates for all childhood diseases below 95%, with 14 counties falling below 90%, according to the health department data. The immunization rate for measles was higher, but 16 counties — or more than 1 in 4 — still reported a rate below 95%.
The lowest immunization rates were in northern California. In Glenn and El Dorado counties, fewer than 80% of kindergarten and transitional kindergarten students were fully vaccinated, and fewer than 81% against measles. Sutter County reported the lowest vaccination rate overall at 73%, and 75.8% for measles.
Southern California has generally fared better. Of the nearly 130,000 kindergarten students in Los Angeles County, more than 97% received two or more doses of the MMR shot last year, the data show. And Orange County reported a 97.4% immunization rate for its nearly 44,000 kindergarten students.
But San Diego County, which has the second-largest number of kindergarten students after L.A. County, saw its immunization rate slip just below the 95% herd immunity benchmark to 94.8%.
In Kern County, the measles immunization rate among more than 19,000 kindergarten students was just shy of 91%, a drop of more than 1 percentage point from the year before, the data show. About 87.4% of kindergarten students had received all their required shots.
Michelle Corson, a spokeswoman for the Kern County Public Health department, said in a statement that a “mistrust of healthcare providers and systems, along with the spread of vaccine misinformation” has contributed to vaccine hesitancy.
She said some residents also face other barriers in accessing healthcare, including lack of insurance or transportation challenges. Corson said the county has run back-to-school vaccination drives and has a mobile health clinic that travels to more rural areas of the county to provide shots.
In Santa Cruz County, 91.8% of kindergarten students were vaccinated against measles last year, a rate that has declined from 94.1% two years earlier, state data show.
“We’re vulnerable,” said Dr. Lisa Hernandez, the county’s public health officer. Scenic Santa Cruz has a “baseline vulnerability” to infectious diseases such as measles, she said, because a relatively high number of people travel through the county to take vacations and to visit the University of California campus.
Many counties with relatively low vaccination rates have a higher share of students enrolled in independent study or home-school programs that do not involve classroom instruction or who receive special education services at school even if they’re not fully vaccinated.
Kern County said 9% of kindergarten students were enrolled in such programs. In El Dorado County, nearly 20% of students were, while in tiny Sutter County, which has the state’s lowest vaccination rate overall, that share surged to nearly 1 in 4 of the county’s kindergarten students.
Heather Orchard, an immunization specialist and public health nurse with El Dorado County Public Health, said despite the rural county’s low vaccination rates, the risk of a measles outbreak is less likely than in larger, more populated counties.
“I feel like our risk is low in El Dorado County,” she said. But, she said, the county is still working on making vaccines available and sharing that information with families who are sending students to school.
California first tightened its childhood vaccination laws a decade ago after a measles outbreak at Disneyland, which spread to 131 people in California, highlighting the risk of a disease that was once thought eliminated. California has reported five measles cases in 2025.
In 2015, state lawmakers approved Senate Bill 277, which eliminated parents’ ability to cite their personal or religious beliefs as a reason for skipping childhood vaccinations that were required for school. That law led to a 5 percentage point increase in the state’s vaccination rate, data show.
Four years later, amid allegations that a handful of doctors were issuing bogus medical exemptions for unvaccinated children, legislators passed SB 276, giving the state more authority to scrutinize those exemptions. Those collective efforts reduced personal belief exemptions to zero and medical exemptions to less than 1% statewide.
But since then, the vaccination rate for all childhood immunizations and for the two-dose measles shot have declined, state data show.
Former state Sen. Richard Pan (D-Sacramento), a pediatrician who wrote both of California’s vaccine laws, said his efforts have made schools safer for vulnerable kids, even while acknowledging that immunization rates remain low in certain regions.
“From a policy point of view, we’ve done what we can,” Pan said. “And I feel that we’ve done well.”
But public health experts are preparing for childhood immunization rates to continue declining in the current political climate and as the anti-vaccine movement becomes more mainstream.
“Now it has started to become much more of this kind of red state, blue state thing,” said Richard Carpiano, a public policy professor at the UC Riverside who has studied vaccine hesitancy.
Carpiano and other experts said there’s general concern that the Trump administration’s decision to pull funding for public health efforts and medical research will only worsen health disparities across the country. He noted that instead of encouraging families to vaccinate their children during this recent measles outbreak, Robert F. Kennedy, Jr., Trump’s U.S. Department of Health and Human Services secretary, promoted vitamin A and cod liver oil as effective treatments.
“We’re going backwards. And we’re creating all these different types of vulnerabilities,” Carpiano said. “The lighter fluid has just been thrown all over these little sparks about freedom and personal choice and parental rights.”
