It’s back-to-school season. For most parents of the U.S.’s school-aged kids, that means filling out medical forms and making sure the children are up to date with their vaccinations. But this ritual is shifting: The 2025–2026 school year saw a record low number of kindergartners vaccinated for measles, polio, tetanus, and more. At the same time, more kids in this age group had exemptions from at least one vaccine that school year than at any other point in the past decade.

Meanwhile the diseases these vaccines protect against are making a comeback. Take measles, for example: The U.S. officially eliminated the disease in 2000 with the combined measles, mumps and rubella (MMR) vaccine. But in the past few years, that progress stalled, and measles is on the rise. So far this year, officials have recorded more than 2,500 measles cases in the U.S.—the most since the virus was wiped out in the U.S. 25 years ago.

We analyzed the latest vaccine data to better understand what states in the country are most at risk of an outbreak and how vaccination rates are changing among the U.S.’s schoolkids.

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How Vaccine Rates Are Changing among Kindergartners

More than 90 percent of U.S. kindergarteners still get the MMR vaccine. But according to the latest data from the U.S. Centers for Disease Control and Prevention, MMR vaccination rates among kindergarteners have fallen from about 95 percent to 92.4 percent in the past 10 years. The country saw similar declines for vaccines that protect against polio, hepatitis B, and diphtheria, tetanus and acellular pertussis.

For the most contagious diseases, even a small dip in vaccination can trigger population-wide problems. “Measles is the single most contagious disease that we know of,” says Adam Ratner, a professor of pediatrics and microbiology at New York University. “It is more contagious than flu or COVID or polio or Ebola or anything else you can think of.” Around 90 percent of unvaccinated people exposed to the virus will become infected.

In most states, specific childhood vaccinations, including MMR, are required to attend public school. Depending on state policy, parents may be able to opt out of certain or all vaccines by claiming an exemption for medical, religious or philosophical reasons. Nationwide, the proportion of kindergartners with nonmedical exemptions has doubled in recent years—from about 1.9 percent 10 years ago to 4 percent today.

How States Break Down

Not all states are equal. Many have seen sharp declines in vaccination rates—kindergarten MMR vaccinations in Idaho, for instance, has seen a drop of 15 percentage points in the past decade. Others have remained mostly stable or even increased, however. In the past 10 years in Connecticut, for instance, kindergarten MMR rates have increased from 96.7 percent to 98.6 percent in the 2025–2026 school year. In Maine, rates have risen from 94.9 percent to 98 percent over the same period. And in New York State, rates have stayed relatively flat over the past decade, with a slight rate uptick from 97.3 percent to 97.7 percent.

In general, states that don’t allow personal exemptions have higher vaccination rates, says Lori Handy, an associate director at the Vaccine Education Center at the Children’s Hospital of Philadelphia. (About two thirds of states don’t allow personal exemptions, although only four states prohibit both personal and religious exemptions.)

That doesn’t mean outbreaks of diseases such as measles don’t or won’t happen in these states. Even in places with the highest vaccination rates, pockets of unvaccinated people can enable viruses to spread. Virginia, for instance, has an overall MMR vaccination rate above the national average. But it’s also seen 177 measles cases this year.

Why Vaccines Rates Are Still in Decline

A county’s or state’s total vaccination rates may reflect a combination of state and local laws, community customs, individual beliefs—and the influence of antivaccine rhetoric. Vaccination rates began to dip after the COVID pandemic. The emergence of this trend was in part because of the challenges of getting to a doctor’s office during that time but was also likely driven by a wave of vaccine skepticism.

“We’ve seen, really, just a shift in the American public in terms of individuals who have lower trust in the health care system, more skepticism around vaccines [and] a lot more misinformation around vaccines,” Handy says.

That misinformation is hard to ignore when it is coming from the highest echelons of power. The new CDC data were released just days after President Donald Trump signed an executive order seeking to break up the MMR vaccine into separate shots for the three diseases it protects against, a change that health experts say would only confuse and discourage parents from getting their children vaccinated. The overwhelming evidence shows that the MMR vaccine is safe and effective as a single shot.

“All parents—regardless of their feelings about vaccines—nobody wants harm to come to their kids. It makes the job of a parent very difficult if you have people on the news, people in the newspaper, people high up in government who are stoking doubt about vaccines,” Ratner says.

Now, as millions of families get back to school—and back to germs—Ratner and Handy both recommend that parents speak with their children’s doctors about any vaccines they may need.

For children who can’t be vaccinated for medical reasons or pregnant teachers and family members, a lack of herd immunity can be life-threatening, Handy explains. And for unvaccinated families, it poses a health risk, as well as the possibility that children will need to isolate at home for several weeks. Vaccinated families generally don’t need to worry about those risks, she adds.

“The lower the vaccination rates are, the more we anticipate outbreaks,” Handy says.