Nearly 150 people have been infected with measles in Texas and New Mexico, and last week, Texas health officials confirmed the first death in the ongoing outbreak: an unvaccinated child. While almost all of the infected are believed to be unvaccinated, five of them told the Texas health department they have received at least one measles shot.

The United States declared measles eradicated in 2000 because the disease was no longer spreading locally (most cases in the following years were linked to travel to countries where the virus was still prevalent) But in recent years, outbreaks of the measles have been growing as more people across the country opt not to vaccinate. The recent reports of cases even among vaccinated people have added another layer of anxiety to the crisis. More than 90 percent of Americans got their measles shot as a kid. Exactly how reliable is that protection, given this news?

First of all, there is no need to panic. It is not clear whether the five people who contracted measles were vaccinated as children. The Texas health department told me they were investigating, but they “wouldn’t classify” these as breakthrough infections. Lara Anton, a department spokesperson, told me unvaccinated people who have been exposed to measles are given a vaccine within 72 hours if possible because it could reduce the severity of their symptoms. 

“We are looking into how many of these cases received a dose of MMR after they were exposed to the virus,” Anton said.

To be clear, breakthrough cases can happen. But the risk today remains very low — only about three in 100 people who receive two vaccine doses get sick when exposed. As Aaron Milstone, an infectious disease pediatrician at the Johns Hopkins University School of Medicine, put it to me, you don’t really have anything to worry about right now if you don’t live in west Texas or eastern New Mexico.

“We don’t want everyone to go out and think, I need to get boosted,” Milstone said.

But if you do live in those areas or you’re not sure of your vaccine status or you simply want to be proactive about your health, there are some things you can easily do to check on your measles immunity. Here’s what you should know.

Why breakthrough measles cases happen

Our measles protection strategy has evolved over the decades. People born before 1957, shortly before the first measles vaccine was introduced, are generally thought to have natural immunity because they were usually exposed to the virus as children. Those born before 1989 likely received at least one dose, which was the guidance during that period. After 1989, the recommendation increased to two doses, one around your first birthday and another around age 5.

That change was made because a small percentage of people did not respond to only one measles shot. But “almost everybody” responded to two doses, Milstone said.

As measles outbreaks become more common and more vaccinated people become exposed naturally for the first time in a long time, some small number of them may get sick, Milstone said.

And, for a long time after that, measles vaccination rates were very high, above the 95 percent threshold experts say is necessary to keep the disease at bay. As a result, measles wasn’t spreading widely within the US and most years saw zero or at most a handful of deaths caused by the virus.

But measles vaccination rates have been declining. There had always been small insular communities that abstained from vaccinations; the current Texas outbreak has reportedly been primarily concentrated in a Mennonite community. But vaccine hesitancy has become more mainstream, particularly as it’s been embraced by some Republican leaders; several GOP-led states have acted to allow more vaccine exemptions in recent years. The share of Republican voters who think routine childhood vaccinations should be required to attend public school has dramatically fallen off since the pandemic.

In the 2019–2020 school year, 20 states were still above the 95 percent vaccination rate threshold and just three had dropped below 90 percent. But for the 2023–2024 school year, only 11 states had more than 95 percent of schoolchildren vaccinated against the disease and 14 states had fallen under 90 percent.

It’s no surprise then that we’re seeing more measles outbreaks. The Texas outbreak alone already accounts for more than half of the total number of US measles cases in 2024, which was itself one of the most active years in recent memory.

It is possible that measles immunity in some people can wane over time. As measles outbreaks become more common and more vaccinated people become exposed naturally for the first time in a long time, some small number of them may get sick, Milstone said.

What you can do to make sure you’re protected

As Milstone told me, this remains a hypothetical risk for the vast majority of Americans, unless you are near an active outbreak. For now, the outbreak spreading at the Texas-New Mexico border is pretty contained.

Even so, we are now living in a world where you are more likely to see a measles outbreak in your community. Other people may simply want to be assuaged or to exercise some agency about their own health — especially if, for example, they are at higher risk from viral infections because they are immunocompromised or have chronic health conditions.

Here’s what you can do. First, check your vaccination records if you can find them. If you did receive two doses, you almost certainly had an immune response. If you received one dose, you probably did too, but it is a bit more likely that measles immunity never took, Milstone said. For those in this group, considering a measles booster is reasonable.

Either way, the next step if you want to investigate further would be to talk to your doctor (as always, with anything regarding your health). They can administer a “titer test” that measures the measles antibodies in your body. If they’re still present — great, you’re protected. If they’re not, you can talk to your doctor about getting an additional measles shot.

This is a new era for public health. Milstone said he and his fellow infectious disease doctors could not believe it when they heard the news of a child’s death from measles in the United States.

It remains entirely preventable by getting vaccinated. And if you are not sure about your immunization, you can take these simple steps to figure out your status. With the death of a school-aged child last week, the stakes are unfortunately all too clear.

“You hope people don’t have to die for others to take this seriously,” Milstone said.

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