More than two-thirds of American counties that collect data on kindergarten measles vaccinations no longer have herd immunity against the disease, and 77% of those counties have seen a decline in immunization rates since 2019. That’s the alarming analysis of school vaccination rates by the NBC News Health & Medical Unit in collaboration with Stanford University.

That’s in contrast to the picture in California. NBC 7 Investigates reviewed data from the Department of Public Health, which shows state laws have largely been successful in ensuring children get the vaccines required for them to attend public and private schools in person. However, the data also reveals declines in the percentage of kindergartners who have all their vaccines.

To attend any in-person instruction at a school in California with at least six students, kindergartners must get:

  • Fpur doses of the polio vaccine
  • Five doses of the diphtheria, tetanus & pertussis vaccine 
  • Three doses of the Hepatitis B vaccine
  • Two doses of the measles, mumps & rubella (MMR) vaccine 
  • Two doses of the varicella vaccine

The requirements impact kids at public schools, charter schools, private schools and even hybrid schools that combine virtual learning with just a couple of days inside a classroom.

California law mandates that students can’t attend school until they are fully vaccinated, unless they can provide an approved medical exemption or have a special circumstance in which they’re given a grace period to get shots.

Protecting the community from a measles outbreak

Health experts use the term “herd immunity,” meaning that enough people are vaccinated against a disease that infection can’t spread. For measles, that target number is 95%. 

NBC News found that 68% of counties that collect data on MMR rates now have rates below 95%. There is a better picture in San Diego County, where schools reported 94.8% of kindergartners had their measles vaccines during the 2023-24 school year, the most recent data available to us. 

“I think it’s one of the most important ways to keep them safe,” parent Cameron Barton told NBC 7. “To think about us doing the right thing, and then another parent not doing the right thing and not getting them vaccinated, and our kid getting sick because of that, it’s scary.”

Unfortunately, dozens of schools in the San Diego area had kindergarten vaccination rates that fell below herd immunity. In 2023, 46 schools fell below 95%.

Erik Berg, San Diego County’s Assistant Medical Director of Epidemiology and Immunization Services, has been watching those declines nervously.

“We are seeing that trend in San Diego County, and, really, this is a trend across the United States, of decreasing vaccination rates coming after the pandemic,” Berg said. “It’s heartbreaking to see a child who is admitted to a hospital or that dies from a vaccine-preventable illness.”

As of Sept. 2, the Centers for Disease Control and Prevention reported 1,431 measles cases, 35 outbreaks, and 3 deaths in 2025. 

Last month, San Diego County announced its first confirmed measles case of the year: an unvaccinated teenager who traveled overseas. Last year, the county reported four cases.

“It’s pretty clear that as vaccinations decline, we’ll see more cases,” Berg said.

How California tracks student vaccinations

A school’s vaccination rate doesn’t mean students don’t have their shots for the entire school year. California requires schools to report student vaccination rates for kindergartners annually, by mid-December. 

Schools don’t submit updated numbers to the state after non-compliant students get their required vaccinations. They just need to confirm vaccinations for those kids before they allow them to attend.

The percentage of unvaccinated students also doesn’t mean a school is operating below herd immunity.

A hypothetical school with an 8% unvaccinated rate includes students with permanent medical exemptions, students who are enrolled at the school but don’t attend in-person classes and other special circumstances.

The latest data available from the state is from the 2023-24 school year. You can see what a local school’s vaccination rate is below:

Avoiding vaccinations

As vaccination rates decline nationwide, vaccine exemptions are rising. NBC News found that 53% of American counties saw rates double from their first year of data to their most recent.

That’s not a problem here in California, which banned personal-belief exemptions in 2016. 

The previous year, 3.6% of San Diego County kindergartners used that type of exemption to avoid shots, and another 0.2% used a medical exemption. In 2023, medical exemptions accounted for just 0.1%.

Medical exemptions spiked locally and statewide after the personal-belief exemption went away but have since bottomed out after the state instituted an online verification system that physicians must use.

The only schools that don’t require vaccinations are home schools and private schools with five or fewer students. The number of students attending these types of schools has been trending upward since personal belief exemptions were outlawed. There was also a spike during the pandemic.