A cluster of measles cases in the Northeast is putting a spotlight on how easily the highly contagious disease can spread — and how dangerous any further slip in childhood vaccination rates could be.

It takes only a handful of measles cases to make headlines. That’s because infants and toddlers not old enough to have been fully protected through vaccination are vulnerable to the virus. Kids don’t get their first shot until they are at least 12 months old and aren’t fully vaccinated until their second dose, given somewhere between ages 4 and 6.

But these days, clusters of cases like those sprinkled across Philadelphia, Wilmington, Delaware, and Camden County in New Jersey feel even scarier thanks to weakening support for routine childhood vaccinations. An increasing portion of the public seems to consider vaccination a choice rather than an obligation.

And of all the vaccines to skip, the routine combination shot for measles, mumps and rubella (MMR) is a headscratcher. Side effects from the shot are mild and similar to other immunizations — redness at the injection site, a fever or mild rash. Meanwhile, measles can spread like wildfire among the unvaccinated, and it hits people hard. Beyond the pain and discomfort of a high fever and body-wide rash, there’s a high risk of hospitalization: In an outbreak last winter in Ohio, 42% of the 85 measles patients ended up in the hospital. In other parts of the world, where vaccination is less readily available, measles killed some 136,000 people, primarily kids, in 2022.

The safe and inexpensive MMR shot acts kind of like a forcefield against other infections, too. In the last two decades, scientists have shown measles wreaks havoc on the immune system of an unvaccinated person, making the body “forget” how to fight off other pathogens by knocking down levels of antibodies against them.

This “immune amnesia” can render someone vulnerable for months or even years, and helps explain why some people infected with measles die from a secondary infection — and why the world saw a puzzling drop in rates of deaths from a range of other conditions after measles vaccination became commonplace.

Given the value of the vaccine, it’s mindboggling that some in the U.S. would choose not to protect their children. And yet, vaccine rates among U.S. kindergartners fell for the second consecutive year in 2022, a situation the Centers for Disease Control and Prevention said left some 250,000 kids vulnerable to measles. While some of those missed shots were potentially due to challenges accessing timely health care during the pandemic, there’s reason to worry that growing hesitancy about vaccination is also at play.

It does not help that some states are making it easier to forgo routine childhood vaccines. Mississippi, for example, previously led the nation in vaccination coverage for kindergarteners, with more than 98.6% of kids in the 2021-22 school year having received both doses of their MMR shots. But anti-vaccine activists succeeded in loosening the state’s childhood vaccination policy, and last year families could for the first time seek religious exemptions for basic shots like MMR, tetanus, polio and others. According to a report from NBC, the state granted more than 2,200 exemptions in the first five months they were allowed.

The shift seemingly reflects a new partisan divide. A recent Pew Research Center poll found a steep drop in the number of Republicans and people who lean Republican who don’t believe vaccines should be required for attending public school.

This is part of a broader, worrisome trend when it comes to vaccination. Differences in opinion along party lines on the safety and benefits of the Covid vaccine have been stark. And that gap now extends to other vaccines, too: A KFF poll from September found that 76% of Democrats would “definitely” or “probably” get a flu vaccine, whereas just 51% of Republicans were so inclined.

That’s showing up in vaccination rates for kids. Fewer parents are seeking out a flu vaccine for their kids this season — an issue not just because kids can get sick, but because vaccinating kids can help protect the elderly. By the end of 2023, just 43.9% of U.S. children had gotten the shot, down from 49.2% at the same time last year — and continuing a five-year downward trend from the 54.1% vaccinated against the flu in the 2019-2020 season. Meanwhile, 13 children died from the flu in the first week of 2024.

In a recent editorial in JAMA, Food and Drug Administration officials asked whether the country had reached a tipping point when it comes to vaccination. How scary to be seriously pondering that question. The authors, Robert Califf, commissioner of the FDA, and Peter Marks, director of the Center for Biologics Evaluation and Research, suggest the “best way to counter the current large volume of vaccine misinformation is to dilute it with large amounts of truthful, accessible scientific evidence.”

In the current climate, that would seem easier said than done. Physicians, who are on the front lines of convincing parents of the benefits of childhood vaccines, would benefit from more training so they are better equipped to have hard talks with parents that push back on vaccines.

In the meantime, maybe everyone would benefit from a reminder of the sizable toll measles used to take on kids in the U.S. — and of the layers of benefits that follow vaccination.

Lisa Jarvis is a Bloomberg Opinion columnist covering biotech, health care and the pharmaceutical industry. Previously, she was executive editor of Chemical & Engineering News.