A PRESS RELEASE ABOUT KIDS AND VACCINES that the CDC distributed on Monday had just three sentences. But wow, those three sentences said a lot—about how we are backsliding on vaccination, and how the Trump administration is about to make things even worse.

The first two sentences initially seemed innocuous, maybe even a little encouraging. They explained that vaccination rates for kindergarteners “remain high,” with just a tiny drop-off between the 2024–25 and 2025–26 school years. But if you clicked through to the data, you learned that there has been a substantial rise in exemptions—that is, families opting out of school vaccination mandates, citing either medical necessity or, in states that allow it, personal beliefs.

Overall, 4.2 percent of kindergarteners had exemptions for at least one vaccine normally required for school attendance. That was up from 3.6 percent the previous year. The jump of 0.6 percent might not seem like much, but keep in mind that it is a national average, meaning that it masks wide variation among the states.1 The highest exemption rate was in Idaho, where 17 percent of parents opted out of the requirements.

Statewide vaccination rates also had that kind of variation. In many states, more than 98 percent of kindergartners had gotten the MMR vaccine, which protects against measles, mumps, and rubella. But in the states with the lowest rates, far fewer did: Idaho, again at the bottom, saw just 75 percent of kindergartners get it.

The scientific term for that is “yikes.”

And just as the national numbers mask variation among the states, the statewide numbers mask variation within their borders. MMR rates in some communities are well below the 95 percent level that’s become the scientific shorthand for “herd immunity,” meaning protection sufficient to stop sustained transmission when isolated cases appear. It is in these communities that outbreaks have driven this year’s measles count past 2,500, the highest in thirty-five years, with more than four months of calendar still to go.

And it’s not just measles. Although pertussis case numbers were down in 2025 from a year earlier, the tally remains higher than before the pandemic, with falling vaccination rates believed to be a significant factor.2 And last year there were sixteen related deaths. Babies are also dying from brain bleeds after their parents spurned vitamin K shots that would have prevented them, as ProPublica reported earlier this year.3

Against that backdrop, Monday’s data release would have been an obvious opportunity for the CDC to encourage vaccination, as part of a broader and aggressive public relations push. But there has been no such push from administration officials, including new CDC director Erica Schwartz, and the only advisory in Monday’s press release was its bland final sentence: “CDC continues to encourage parents to discuss vaccination options with their doctors.”

That mantra should sound familiar. It has been the agency’s party line under Robert F. Kennedy Jr., who has been undermining federal support for vaccines ever since taking over as health and human services secretary last February. And he’s been doing so with the full support of President Donald Trump, whose own medically illiterate skepticism of vaccines was on full display last week during an Oval Office ceremony to sign an executive order.

An underappreciated element of that order is an instruction to federal agencies, calling on them to scrutinize and pressure states that make it difficult for parents to take exemptions—yes, the very trend that Monday’s press release documents. Among the agencies the order mentioned was the Justice Department, in what has been widely interpreted as a promise to start or join litigation against states that, in the Trump administration’s view, don’t make exemptions appropriately easy to obtain.

California is almost certainly one of those states, because exemptions there are especially tough for parents to get. But that wasn’t always the case. California’s vaccine rules are stringent because lawmakers made them that way. And they did so following a measles outbreak a decade ago—one that offers a preview of what’s in store for the rest of the country if the Trump administration’s latest effort succeeds.

IN EARLY JANUARY 2015, California’s state health department started getting reports of suspected measles cases from doctors and clinics. First it was one, then a half dozen, then dozens. Public health investigators got to work and quickly found a common element: All of the initially affected people had been to the happiest place on earth—i.e., Disneyland—just before Christmas.

The resort’s theme parks were a perfect environment for the disease to spread, as a subsequent Los Angeles Times article detailed, especially with the peak crowds from the holiday season. Standing in packed indoor queues for rides and shows, kids and adults were swapping breath and droplets for long enough to pick up a virus that can linger in the air for up to two hours, and that infects about nine of ten susceptible people who encounter it.

Except, that is, when they are vaccinated. The full, two-dose MMR vaccine is 97 percent effective at preventing measles, and symptoms in the breakthrough cases tend to be milder. The overwhelming majority of cases in the 2015 outbreak—both those who picked up the disease in Disneyland and those who got it afterward through secondary transmission—either had not been vaccinated or had unknown vaccination status.

California lawmakers responded quickly, in part because they were already paying attention. In 2012, following a decade in which the number of non-medical exemptions had risen from 4,000 to nearly 15,000, the legislature had passed a law making the process of obtaining an exemption a bit more complex: Instead of simply signing a piece of paper saying they had a principled reason for objecting, parents had to show they’d gotten information from a health provider about the risks and benefits of immunization (like avoiding the possibility of disability or death from measles).

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To lawmakers like Democratic state senator Richard Pan, a pediatrician, the Disneyland outbreak was proof that California needed to do more. Pan cosponsored a bill eliminating non-medical exemptions altogether, arguing—in a neat reversal of anti-vaxxers’ libertarian rhetoric—that the legislation was “about freedom; freedom from deadly contagions that are now preventable because of vaccines.” The bill drew plenty of angry opposition, enough that Pan got extra security. But the bill passed and became law with the signature of Jerry Brown, California’s Democratic governor.4

Four years later, following reports that some doctors were signing exemption forms without good clinical reason and sometimes without even seeing patients, lawmakers passed a bill tightening the medical exemption standard. Under the new legislation, which Democrat Gavin Newsom signed and is still in force today, the state tracks medical exemptions through a central system that requires doctors to attest that they’ve evaluated the patient and have a clinical basis for the exemption.

There’s solid evidence the laws had the effect their champions had hoped for. Before 2015, the MMR vaccination rate for California kindergartners was just above 92 percent, according to official state data. Since 2016, it has been at or above 95 percent for every year.

That’s not 100 percent, obviously. And the rate has actually declined by nearly a percentage point over the past few years, in a reminder that official requirements are just one of the factors determining vaccine takeup.5 But at least some of the parents opting out of vaccines for non-medical reasons are homeschooling their children, reducing the opportunities for spread within schools. And the state’s overall high vaccination rates are making outbreaks less likely.

That sounds a lot like a successful public health effort. Now the Trump administration seems bent on undermining it, possibly through the courts.

FOUR OTHER STATES also have no religious exemption for school vaccine requirements. And like those four states, California has faced litigation from anti-vaccination groups, religious freedom advocates, and parents who say that’s illegal. The Justice Department could join those lawsuits, or launch new ones.6

To date, lower federal courts have issued inconsistent, sometimes conflicting rulings in cases before them, University of California, San Francisco law professor Dorit Reiss told me in a phone interview. And the Supreme Court has so far declined to take up the issue directly.

But Reiss said that could change, noting that the justices have already vacated a lower court decision backing New York’s strict vaccine laws. In that 2025 ruling, the Court’s conservative majority instructed the lower court to take up the case again, this time taking into account a recent decision recognizing parents’ rights to pull their kids out of LGBTQ-inclusive lessons for reasons of religious faith.

And Justice isn’t the only cabinet department that Trump commanded to focus on vaccine exemptions. Under the executive order, the Department of Education can withhold grants to states that don’t allow exemptions easily enough to meet the administration’s standards. And while any attempt to cut off funds would likely provoke legal challenges from states like California, it might push other states with strict vaccine requirements in the other direction.

West Virginia is a perfect example. It is one of the four other states with no current religious exemptions and, as of the 2025–26 school year, it had the nation’s highest MMR vaccination rate: almost 99 percent. But bills that would reinstitute religious exemptions or roll back vaccine mandates in other ways have been gaining strength in the legislature. And the governor has already tried to introduce religious exemptions via executive order, though a federal court has for the moment blocked him.

The threat of litigation or lost funds, not to mention anti-vaccination lobbying from the Trump administration, could help the sponsors of those bills rally majority support.

“I know that my immunization colleagues in red states are worried,” said Reiss, who is a widely cited expert on vaccination law. “They expect legislation to be brought—and they expect pressure to pass it—that would either weaken vaccine mandates or weaken vaccine recommendations following the federal guidance.”

A glimpse of what could be in store for West Virginia comes from Mississippi, where MMR vaccination rates have fallen from 99 percent in 2023 (then the highest in the nation, just above West Virginia) to 97 percent (sixth highest). One reason is the introduction of religious exemptions, after a federal judge sided with plaintiffs who said the state’s lack of faith-based exemptions violated their freedom of religion. More than 3,500 students received the exemptions last year, nearly six times the number claiming medical exemptions.

State Health Officer Dan Edney told Mississippi Today that more measles outbreaks are “inevitable” as vaccination rates fall. That’s true for the rest of the country, as well. Evidently that trend is just fine with the Trump administration, where the only alternative to doing nothing is making the vaccination situation worse.

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