With measles on the rise in the U.S., here’s how to know if you’re adequately protected
By Kevin Loria
A measles outbreak that began in January has sickened hundreds of people, with smaller outbreaks and scattered cases across the U.S., from Florida to Alaska. At least two children have died.
With cases of the highly contagious virus popping up around the country, it’s a good time to consider whether you are adequately protected, says Tina Tan, MD, a professor of pediatrics at Northwestern University’s Feinberg School of Medicine in Chicago and president of the Infectious Diseases Society of America.
Though many Americans are fully protected, some may benefit from a booster dose, depending on when you were vaccinated, whether there is an ongoing outbreak nearby, and whether you’ve undergone certain medical treatments (such as a bone marrow transplant) that can eliminate previously acquired immunity.
Here’s how to tell whether a measles booster makes sense for you. (To learn more about when it makes sense to give an unvaccinated baby an early shot, see our previous article.)
Why Measles Is So Risky
Measles is one of the most contagious viruses we know of, according to Amy K. Winter, PhD, an assistant professor of epidemiology and biostatistics at the University of Georgia College of Public Health in Athens, who spoke at a March press briefing hosted by SciLine.
In a community with no immunity, each case of measles would be expected to spread to 12 to 18 other people, making it more contagious than the flu, chickenpox, or COVID-19. A measles infection can be severe. Before the vaccine was introduced, there were 3 to 4 million infections a year, leading to 400 to 500 deaths, 48,000 hospitalizations, and 1,000 cases of dangerous and potentially damaging brain swelling each year, according to the Centers for Disease Control and Prevention.
A vaccine was first introduced in 1963, with a more effective vaccine introduced in 1968. A 1989 outbreak led to the recommendation that children get a second dose of the vaccine. (One dose of the current measles vaccine is 93 percent effective against measles; two doses are 97 percent effective.) In 2000, the virus was declared eliminated in the U.S., meaning that no single outbreak in the country spread for longer than 12 months. But it has continued to circulate regularly in less vaccinated countries around the world.
Because measles is so contagious, infectious disease experts say that 95 percent of people need to be vaccinated to prevent its spread (from an infected traveler, for example), especially among those who cannot be vaccinated, such as very young infants and immunocompromised people.
Some measles outbreaks happen among Americans every year, usually when a case is imported. And since the COVID-19 pandemic, vaccination rates among kindergarteners have fallen below 95 percent, Tan says. As vaccination rates drop, the risk of outbreaks and sustained transmission rises. Vaccination rates in some communities are far below the required level for adequate protection, providing a vulnerable opening for the current ongoing outbreaks.
Who Doesn’t Need a Booster
If you have had two doses of the current vaccine, you don’t need a booster. This generally applies to people born in the U.S. in 1989 or later.
If you were born before 1957, you also don’t generally need a booster, because it’s assumed that pretty much everyone born before then had measles at some point, and infection-acquired protection is also considered lifelong. There’s one exception: Healthcare workers who were born before 1957 should consider getting a measles booster if they haven’t had one already, because their exposure risk is higher than that of the average person.
Who Definitely Needs a Booster
If you were vaccinated before 1968. People vaccinated before 1968 (between when a vaccine was first introduced in 1963 and 1967) most likely got a vaccine made with an inactivated measles virus, which was less effective than the vaccine that replaced it in 1968. These people should be revaccinated with a modern vaccine, according to the CDC. If you aren’t sure when exactly you got your shot, see the next section for people unsure of vaccine status.
Who Might Need a Booster
If you got just one dose, which was likely the case for people vaccinated before 1990. Most healthy adults in this category probably don’t need another dose, according to the CDC. Whether a booster is necessary here is often decided on a case-by-case basis—talk to your healthcare provider if you think you may qualify. Those who may benefit from another dose include the following:
• Healthcare workers who are at a greater risk for measles exposure than the general public should get a second dose if they don’t have one already.
• Travelers: If you plan to travel outside the U.S. and didn’t get a second dose as a child, talk to your doctor about a potential second dose.
• People in an area with an active outbreak: If you live in an area with an active outbreak, you should get a second dose if you did not get one as a child, Tan says.
• People who live with an immunocompromised person: If someone in your home is immunocompromised, you should get a second MMR dose to help protect them, Tan says. Immunocompromised people are at a high risk of severe complications if exposed to measles, according to the CDC.
If you have received certain medical treatments: Some people may need to be vaccinated again, even if they were fully vaccinated as children. People who have undergone cancer treatment, for example, can sometimes lose immunity to illnesses they were previously vaccinated against. That’s especially true if they underwent certain treatments, including a bone marrow transplant, a stem cell transplant, or CAR T-cell therapy.
If you have gone through cancer treatment, talk to your doctor about whether you need to be vaccinated again, and when you are eligible—they may want to run certain tests to check your immune status, and you’ll need to wait a certain amount of time after completing your treatment before you can get certain vaccines.
If you don’t know your vaccination status: It’s likely your state or the state you grew up in has your vaccination records, and you can try to look them up on a state government website, or check to see if your parents or former pediatrician has your records. If you can’t figure it out, you should just get vaccinated, according to the CDC—especially if you are traveling internationally. Even if it turns out you have been vaccinated and are already immune, receiving another dose is safe.
While it’s technically possible to get a blood test known as a measles antibody titer test to check your immune status, this is generally not recommended. It’s not a reliable indicator of long-term immunity and results may be misleading, Tan says. That’s because titer tests measure only the level of antibodies in blood, but immunity also involves other parts of the immune system, such as memory B cells and T cells. Those play a critical role in protecting against measles and are not assessed by a titer test, so results could suggest you are not adequately protected even when you are.
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