Measles Susceptibility In American Kindergartners Has Risen By More Than Half Since 2019
SPARTANBURG, SOUTH CAROLINA - FEBRUARY 6: South Carolina State Rep. Rosalyn Henderson-Myers (D-Spartanburg) stands outside a mobile clinic offering free measles vaccinations on February 6, 2026 in Spartanburg, ...
SPARTANBURG, SOUTH CAROLINA - FEBRUARY 6: South Carolina State Rep. Rosalyn Henderson-Myers (D-Spartanburg) stands outside a mobile clinic offering free measles vaccinations on February 6, 2026 in Spartanburg, South Carolina. The clinic offered free MMR vaccinations as the South Carolina Department of Health reported 876 cases of measles earlier in the week, most centered in Spartanburg County. (Photo by Sean Rayford/Getty Images)
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The CDC has released its kindergarten vaccination data for the 2025-26 school year, along with a statement three sentences long. Coverage among kindergartners “remained high,” it said, and the latest figures showed a decline of a tenth of a percent from the year before.
Neither the statement nor the figure describes the risk in any particular school, because measles spreads school by school, and a national average masks the differences between schools. On August 18, Nature Medicine published the first national database of vaccination coverage for individual American schools.
Vaccine Exemptions Are Up
While coverage fell a tenth of a point year over year, from 92.5 to 92.4 percent, the exemption rate rose from 3.6 to 4.2 percent, the largest single-year increase in fifteen years. An exemption excuses a child from a vaccine the state otherwise requires. The rate climbed in 42 states and D.C., passing 5% in 24 of them. About 157,000 kindergartners now hold one, almost all on non-medical grounds.
Two doses of the MMR vaccine protect about 97% of recipients, so coverage of 92.4% leaves roughly 90% of kindergartners immune. Measles is expected to spread through a school until about 93% of the children in it are immune. National coverage no longer clears that bar.
The share of kindergartners arriving without a complete MMR series was 4.8% in 2019-20 and is 7.6% now, an increase of more than half. Exemptions also cluster geographically, so unvaccinated children tend to sit together in the same schools and the same towns.
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National kindergarten MMR coverage peaked at 95.2 percent in 2019-20 and has fallen every year since, dropping below the roughly 93 percent needed to stop measles spreading in 2021-22 (left). The national figure hides the range underneath it. In 2025-26 coverage runs from 75.2 percent in Idaho to 98.9 percent in West Virginia, and 32 of 50 states fall short of the threshold (right). Data: CDC SchoolVaxView.
John M. Drake
Vaccine Coverage Is Lowest In Private Schools
The database was compiled by Siyu Chen and Ana Bento, researchers at Cornell, over 14 months. It records MMR coverage for more than 50,000 schools, 13,000 districts and 3,000 counties in 45 states and D.C. from 2013 to 2025, compiled from state systems. Part of the information came from a dataset the Washington Post assembled, because no federal agency publishes one.
Three findings come straight out of the data. Coverage grew steadily more unequal across schools between 2013 and 2025, so the national decline landed unevenly and some schools fell much further than the average.
Private schools hold the lowest coverage in most states. South Dakota’s private school median runs 26 points below its public schools, and the lowest private schools in South Dakota and Idaho fall between 40% and 60%.
Homeschooled children never appear in the data at all. They are about 3.4% of American 5- to 17-year-olds, often concentrated in the same communities.
County Averages Hide The Schools Where Outbreaks Start
A county’s coverage figure is the enrollment-weighted average of its schools, and averaging keeps the mean while throwing away the spread. A county reported at 95% might contain twelve schools all near 95%, or one school at 60% and 11 at 99%. An outbreak is much more likely in the second county than the first, although they appear identical in county-level data.
Chen and Bento also built a transmission model, which converts each school’s susceptibility, enrollment and distance from its neighbors into an estimated reproduction number—the number of secondary cases generated by an initial case. Outbreaks may occur in schools with reproduction numbers greater than one.
Given only the coverage recorded the year before each of seven outbreaks between 2017 and 2026, school-level estimates placed all seven outbreak sites in the top tenth of their state’s schools. County-level estimates identified three.
Are There Early Warnings Before Measles Outbreaks?
Epidemiological theory says an outbreak should be visible in surveillance data before it happens. As a population drifts toward the epidemic threshold, it recovers more and more slowly from small disturbances, a phenomenon called critical slowing down. The slowing appears in weekly case counts as rising variance and autocorrelation, a measure of how strongly each week's count tracks the one before it.
We went looking for it in U.S. measles cases from 2006 through 2025 and our paper found nothing. Neither variance nor autocorrelation rose before any of the three major outbreak episodes, in 2014, 2019 and 2025.
We offered four explanations for this finding. One was that national case counts average over places whose epidemics run out of step, and the averaging destroys the signal. Chen and Bento measured that averaging directly.
If combining schools into counties turns a supercritical picture into a reassuring one, combining every county in the country into a single weekly number destroys a great deal more. We looked for autocorrelation in time and found none. They measured inequality between schools and found it growing through the same years.
The share of states with kindergarten MMR coverage below the epidemic threshold sat near 35 percent, with no trend, for the decade before the pandemic. It then stepped up and has settled near 60 percent. The pattern appears to be two stable regimes separated by a shock rather than a steady slide toward the threshold. Data: CDC SchoolVaxView.
John M. Drake
Will The U.S. Lose Its Measles Elimination Status?
The CDC measles page states that kindergarten coverage “has decreased from 95.2% during the 2019–2020 school year to 92.4% in the 2025–2026 school year, leaving approximately 280,000 kindergartners at risk.” Its press office, the same week, said rates remained high.
A national epidemic remains unlikely. Most American adults are immune, so an outbreak burns through the unvaccinated children in one community and then meets a wall of immunity. That is why the ongoing epidemic has produced a few large local outbreaks rather than a wave, with 414 cases in Gaines County, Texas and close to a thousand in upstate South Carolina.
Elimination depends on whether the virus reaches a new pocket before it exhausts the one it is in, and at present it does. As of August 20 this year, the CDC had confirmed 2,777 cases across 47 jurisdictions, more than the 2,289 in all of 2025, and 1,375 of this year’s cases belong to outbreaks that began in 2025 and never stopped.
A country forfeits elimination when transmission runs unbroken for 12 months. The Pan American Health Organization, which certifies elimination across the Americas, rules on the United States in November. The status has stood since 2000.