The number of U.S. kindergartners starting school without being fully immunized continues to rise, as more families forgo the protective shots despite outbreaks of vaccine-preventable illnesses.

The U.S. Centers for Disease Control and Prevention reported Monday that the number of children who were fully up-to-date on their immunizations when they started school in 2025 fell from the prior year, with declines in shots for measles, polio and chicken pox.

Exemptions that allow kids to attend without being fully vaccinated rose to 4.2% for the 2025-2026 school year — hitting a record. Last year, 3.6% of kids had exemptions. The number exceeded 5% in 24 states in the most recent school year.

The U.S. has been grappling with ongoing measles outbreaks that have reached the highest infection levels in three decades. Vaccination levels for measles held up in some of the hardest hit states, with immunization rates dropping nationwide by just a fraction of a percentage point. But coverage varied widely, with 75.2% of those starting school in Idaho vaccinated, compared to 97.7% of those in New York.

Nationwide, 92.4% of U.S. children were vaccinated fully against measles, mumps and rubella in 2025, down from 92.5% the year prior. That’s below the 95% threshold public health experts calculate is needed for herd immunity against measles, which protects those in the community who are immunocompromised or unable to get a vaccine.

The numbers show vaccinations are still broadly popular across the U.S., despite renewed attempts by the Trump administration to alter childhood immunization schedules.

Some states posted increases in MMR coverage as infections led parents to get their kids protected. South Carolina, which recorded the largest measles outbreak with nearly 1,000 cases, saw its MMR vaccination rate jump to 93.4% for 2025 from 91.2% a year earlier.

There’s renewed interest in the U.S. vaccine schedule at the federal level. Last week, President Donald Trump attacked the MMR directly, issuing an executive order to break up the combination vaccine into three separate shots. That could be expensive and complicated for Merck & Co. and GSK Plc, the pharmaceutical companies that make the shots. It also adds to the mounting confusion and raises the risk that some children may miss immunizations.

Vaccine policy in the U.S. has been upended under Health and Human Services Secretary Robert F. Kennedy Jr. Kennedy, a long-time critic of inoculations, fired a key immunization panel last year and then stacked the group with some vaccine critics. He then bypassed the committee to remake the childhood vaccine schedule. Both moves are tied up in court.

Trump’s latest effort came just months before the midterm elections. Previously, Kennedy was directed to avoid the politically fraught topic after internal polling found vaccinations were still largely popular in competitive election districts.

The order directed states to reexamine their vaccine schedules, including adjusting which shots would be required for school attendance.

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