Even a single shot of the MMR vaccine provides substantial protection against measles, but two doses are standard.
Even a single shot of the MMR vaccine provides substantial protection against measles, but two doses are standard. © SamaraHeisz5 via Shutterstock
Measles has been making an unwelcome comeback in the U.S. and world lately. Its resurgence might be enough to make many of us reasonably wonder: Just how protected am I from measles? And should I think about getting a booster vaccine shot?
It’s important to emphasize that the measles, mumps, and rubella (MMR) vaccine is highly effective—providing 97% protection from measles with the standard two-shot series. Most Americans have and are still getting vaccinated with the MMR vaccine, thanks to routine childhood programs that were established nationwide starting in the 1980s.
These programs require children to receive several vaccines to attend public school, but families can obtain medical or personal exemptions depending on the state. As of the 2023-2024 school year, roughly 93% of school-age children in the U.S. have received their MMR shots. That said, this percentage has slightly dipped in recent years and is now below the threshold of herd, or community, immunity needed to prevent the highly contagious virus from spreading widely in any given area. Hence the recent outbreaks.
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The current measles outbreaks in Texas, New Mexico, and Oklahoma, now officially over 500 cases, are occurring almost entirely among pockets of unvaccinated people, and it’s the unvaccinated who are much more vulnerable to measles, particularly very young children. But there are certain situations in which you might want or need a catch-up vaccination.
Walter Orenstein, a professor at the Emory University School of Medicine and former director of the U.S. immunization program at CDC, notes that there were two types of measles vaccine that first became available in the U.S. in 1963.
One was a live, weakened virus vaccine—the same type used today, though later modified to be milder—and the other was an inactivated, or killed, measles virus vaccine. Unfortunately, the inactivated vaccine didn’t provide lasting immunity and increased the risk of a severe form of measles, known as atypical measles, in people who later caught the virus naturally. It was pulled by 1967—but some people who got it are still around today.
“So if someone was vaccinated between 1963 and 1967 with this vaccine, or an unknown vaccine, it’s reasonable to get another dose of the measles vaccine that’s actually effective,” Orenstein told Gizmodo. People who received this vaccine or are unsure of which vaccine they received during this time period are recommended to get at least one dose of the standard measles vaccine.
Practically everyone born before 1957 is likely to have contracted measles, which also provides long-lasting immunity, so they’re generally fine. The Centers for Disease Control has said that healthcare personnel born before 1957 with no evidence of measles infection (either in their records or from lab tests) should consider the standard two-dose series.
It’s also worth noting that Americans born between 1968 and 1989 received only one shot of the MMR vaccine. Even a single shot is highly effective—about 93%—so most people in this scenario are well protected. But the CDC does recommend that adults at higher risk for measles exposure get their second shot if they haven’t already. These higher-risk groups include college students, healthcare personnel, people traveling internationally, and anyone else who’s deemed to be at risk by public health officials, such as people living near active outbreaks.
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The nearly 100% protection provided by full MMR vaccination does still leave open some tiny room for vulnerability, of course. Sometimes, a fully vaccinated person, exposed to measles during an outbreak, will get sick. This might happen because the person’s immune system didn’t mount a full protective response at the time of vaccination, or because a person’s immunity has waned over time.
Thankfully, waning immunity isn’t a major individual concern. Studies have estimated that somewhere between 0.22% and 0.04% of the vaccine’s effectiveness declines yearly. This means it would take between five and 25 years for the average person to be 1% less protected than they were right after their MMR shots.
If you are concerned about your susceptibility to measles, or you don’t know your vaccination status, you can always talk to your primary care doctor. Your doctor might run a blood test to check for measles antibodies—or even proactively recommend an MMR dose. While no one likes a needle, the MMR vaccine is perfectly safe, so getting an extra shot is fine even if you might already be well-protected.
“One of the pluses, if someone happens to be already immune, is that nothing would happen because their bodies would kill the vaccine virus before anything can happen,” Orenstein said.
Outside of a few corner situations, though, measles remains a more serious threat to the unvaccinated, including people who are too young or medically unable to get vaccinated, such as people with severely weakened immune systems. The best way to keep the virus contained, he notes, is to make sure everyone who can get vaccinated does.
“That’s why it’s so critical that we get very high immunization levels in our communities. Because for the measles virus to survive, it needs to be transmitted from an infectious person to a susceptible person. And if the infectious person only comes in contact with immune people, that chain of transmission is broken and indirectly protects people who can’t be vaccinated because they have legitimate medical contradictions—they’re all protected if they’re not exposed,” Orenstein said.
Children are recommended to get their first MMR shot between 12 and 15 months of age, and their second shot between 4 and 6 years of age, though children at risk of exposure during an outbreak or international travel may receive them earlier and/or an extra dose.
Measles is no joke—it’s highly contagious and can be dangerous especially for kids and people who can’t get vaccinated. If you’re at risk, or uncertain about your status, you may want to talk to your doctor sooner rather than later.