Amid conflicting messages over the safety of vaccines, cases of measles have been on the rise both in California and the U.S. this year compared to 2025.
And in the San Joaquin Valley, where two cases of measles have been reported so far in 2026, vaccination rates among kindergarten students at a growing number of schools are falling short of a level considered to provide “herd immunity” to prevent the disease from spreading.
Data compiled and made publicly available by The Washington Post show that, in the 2023-24 school year, 64 public, charter and elementary schools in the Valley had fewer than 95% of kindergarten students who were fully vaccinated – receiving at least two doses of measles vaccine by the time they entered school.
But in the 2024-25 school year, the most recent year for which the California Department of Public Health has published data on county and school-level vaccination rates, of 916 schools in the Valley, the number of schools falling short of herd immunity among their kindergarten students had grown to 81.
Valleywide, all but one county had their respective kindergarten populations with vaccination rates of at least 95%. Merced County and Kings County tied for the highest rate with 97.9% of its children having the required two measles/mumps/rubella shots. Merced County is also the only Valley county where the vaccination rates increased since the 2022-23 school year.
By contrast, Kern County – where the Valley’s only two measles cases of 2026 have been confirmed – was the only county under the 95% threshold. Kern County has fallen below the herd immunity threshold for kindergarten measles vaccinations every school year from 2017-18 through 2024-25.
Countywide kindergarten vaccination rates for measles for the 2024-25 school year were:
- Merced County: 97.9% of kindergarteners fully vaccinated.
- Kings County: 97.9% of kindergarteners fully vaccinated.
- Madera County: 97.7% of kindergarteners fully vaccinated.
- Tulare County: 97.5% of kindergarteners fully vaccinated.
- Fresno County: 97.4% of kindergarteners fully vaccinated.
- San Joaquin County: 96% of kindergarteners fully vaccinated.
- Stanislaus County: 95.6% of kindergarteners fully vaccinated.
- Kern County: 89.3% of kindergartners fully vaccinated.
As more Valley schools see their measles vaccination rates fall short of the 95% threshold, the U.S. Centers for Disease Control reports that nationally, “vaccination coverage among U.S. kindergarteners has decreased from 95.2% during the 2019-2020 school year to 92.4% in the 2025-26 school year, leaving approximately 280,000 kindergarteners at risk. …”
“The measles, mumps and rubella (MMR) vaccine is very safe and effective,” the agency added. “When more than 95% of people in a community are vaccinated … most people are protected through community immunity (herd immunity).”
Lowest individual school rates
Among the schools with the lowest measles vaccination rates among their kindergarten students are online charter schools, representing populations of children who are schooled at home or take online classes rather than attend school at a physical campus.
The lowest MMR vaccine rate in the Valley belongs to Heartland Charter School based in the Kern County community of Maricopa. The school serves home-schooled students not only in Kern County but also neighboring Kings, Tulare, Inyo, Los Angeles, San Bernardino, San Luis Obispo, Santa Barbara and Ventura counties.
In the 2024-25 school year, the school reported a kindergarten enrollment of 810 students, without any breakdown of how many are from each of the counties served. But across its entire footprint, the state Department of Public Health reported that only 4% of its students were fully vaccinated for measles.
Other online or charter schools with kindergarten vaccination rates of less than 25% for measles in 2024-25 were:
- California Online Public Schools Central Valley: chartered in the Alpaugh Unified School District in Tulare County with students from neighboring San Joaquin Valley counties. The state Department of Public Health reports that of 34 kindergarten students, 15% were fully vaccinated for MMR.
- California Online Public Schools Northern California: chartered in the Ripon Unified School District in San Joaquin County with students also enrolled from surrounding counties in the Central Valley and the Bay Area. Of its 46 kindergarten students, 17% were fully vaccinated.
- California Virtual Academy @ San Joaquin: chartered in the New Jerusalem Elementary School District in San Joaquin County with enrollment from surrounding counties. Of 228 kindergarteners, 20% were fully vaccinated.
- California Virtual Academy @ Maricopa: chartered in the Maricopa Unified School District in Kern County with students also enrolled from Inyo and Santa Barbara counties. Of 100 kindergarten students, 20% were fully vaccinated.
- Mountain Home Charter School: chartered in the Yosemite Unified School District in the Madera County community of Oakhurst with enrollment from Madera and Fresno counties. Of 27 kindergarteners, 22% were fully vaccinated.
- Blue Ridge Academy: chartered in the Maricopa Unified School District with enrollment from Kern, Los Angeles and Ventura counties. Of almost 1,100 kindergarteners enrolled, 23% were fully vaccinated.
Among private schools associated with religious institutions in the Valley, none for which data were available had kindergarten vaccination rates lower than 75% for measles.
The bigger picture
Measles symptoms start with a fever that lasts for a couple of days, state health officials said. That is followed by a cough, runny nose, conjunctivitis or “pink eye” and a rash that usually appears on the face, along the hairline and behind the ears before spreading to the rest of the body,
“Those infected can spread measles about four days before their rash starts to four days afterward,” the state Department of Public Health states. “Those exposed to measles should monitor for symptoms like fever and/or rash for 21 days following exposure.”
Measles can cause more serious ailments including pneumonia and encephalitis or brain swelling, and can result in hospitalization or even death.
The Cleveland Clinic, a renowned academic medical center, indicates that measles can also make people sick with other infections as well.
“Before it was part of routine childhood immunizations, measles caused millions of deaths around the world,” the organization’s website states. “There’s no specific treatment or cure.”
The San Joaquin Valley has not been subjected to an outbreak of measles as has been seen this year in other parts of the country. In California, the U.S. Centers for Disease Control reports 54 confirmed measles cases so far in 2026, compared to 26 for all of 2025 and 13 in 2024.
Nationwide, the increase in cases has been stark over the past few years. In 2023, just 59 confirmed measles cases were reported by the CDC across all 50 states. That climbed to 285 cases in 2024, and shot upward to 2,289 in 2025. So far in 2026, nearly 3,500 confirmed cases have been reported. About 95% of those cases are among people who are unvaccinated, while another 3% had only received one dose of vaccine.
Children under the age of 5 account for almost 630 of the 2026 cases; more than 1,500 cases have been among children and young adults ages 5 to 19 years old.
The number of people hospitalized thus far this year is 301, already outnumbering the 244 people who required hospital treatment during the entirety of 2025.
The measles virus is considered highly contagious and spreads when an infected person speaks, coughs, sneezes or breathes, according to the California Department of Public Health.
The U.S. officially declared measles eliminated in 2000, “meaning there is no measles spreading within the country and new cases are found only when someone contracts measles abroad and returns to the country,” the CDC stated.
Tim Sheehan is a senior reporter and Health Reporting Fellow with the nonprofit Central Valley Journalism Collaborative. The CVJC fellowship is supported by a grant from the Fresno State Institute for Media and Public Trust. CVJC research assistants Chloe Lyons and Marisol Herrera contributed to this report. Contact Sheehan at tim@cvlocaljournalism.org.