When I enrolled in graduate school at the age of 53, I knew I would probably be the oldest student in class. But I was stumped by one of the admission requirements – an immunization certificate for the measles, mumps and rubella (MMR) and tetanus vaccines, verified by a doctor.
Fortunately, I had my mother’s handwritten documentation of my vaccines and took this to my primary care physician. “Beautiful,” she said, admiring the yellowed paperwork, which noted one measles vaccine when I was 13 months, the other at 10 years. “But these aren’t official records, so you need a titer test.” Awhat?
Titer tests, my doctor explained, measure antibody levels in the blood. The results threw me for a loop. My immunity to rubella was sufficient, but mumps and measles antibodies were too low, and I needed anMMRvaccine before stepping foot on campus.
It was a simple fix, but the incident lingered in my mind. Why were my titers low for measles antibodies despite two rounds of the vaccine? Withrecord outbreaks this year– 607 in the US as of 3 April 2025 – I wondered if older adults should be concerned.
According to Dr Scott Roberts, a Yale Medicine infectious disease specialist, adults who were immunized against measles between 1963 and 1967 – as I was – are at risk. During that period, said Roberts, children received either an inactivated measles vaccine or a live one. The inactivated version was less effective; it was discontinued in 1967.
According tothe Centers for Disease Control and Prevention (CDC), nearly 1 million people in the US received the inactivated vaccine between 1963 and 1967. (It was tested in clinical trials in the UK but never put into widespread use.) Per my mother’s records, my second measles vaccine was live, but the first one, administered at the end of 1967, was not, which could explain the low titers test.
If you know you received the inactivated vaccine, said Dr Aniruddha Hazra, a UChicago Medicine infectious disease expert, or don’t know which one you got in the 1960s, “get the MMR vaccine again. There is no harm in getting the shot even if you are fully immunized.”
Adults can confirm immunity with a titer test, like I did, but the test can cost more than the MMR vaccine. “If you would rather get the titers checked first,” said Hazra, “that’s a conversation to have with your healthcare provider.”
But a low titer test doesn’t necessarily mean you’re susceptible to infection. Dr Robert Bednarczyk, an associate professor of global health and epidemiology at Emory University’s Rollins School of PublicHealth, explained that even if vaccinated individuals don’t have detectable circulating antibodies, they probably have memory cells in their immune system ready to produce more antibodies against the virus.
Before the measles vaccine was introduced in 1963, measles was a major cause of death in children under five. Infection could lead to hearing loss, deafness or debilitating neurological side effects. What is the current recommendation for adults born before the vaccine?
“Anyone born before 1957 was exposed to measles,” said Hazra. “Based on that, the CDC and ACIP [Advisory Committee on Immunization Practices] said we can assume you were exposed or acquired measles, and measles immunity is lifelong.” This means no additional vaccine is recommended for this age group.
If you’re wondering how many shots you should have had, the answer is slightly muddy.
Until 1989, the CDC recommended only one dose of the MMR vaccine for children. Thereafter, a second MMR dose was recommended to help “increase the immune response in the small number of people who didn’t fully respond to the first dose”, said Bednarczyk.
The CDC currently recommends two doses of the measles vaccine for children and “one or two” doses for adults, reserving the two-dose recommendation for adults identified as high-risk, such as those in higher learning and healthcare settings, or who are traveling internationally.
“One dose is very effective at preventing measles,” said Bednarczyk. “This is important, because many people born before the mid or late 1980s likely only received one dose of the MMR vaccine.” But, he added, people vaccinated prior to the two-dose recommendation benefited from high MMR vaccine uptake, which greatly reduced the risk of large measles outbreaks.
The vaccination landscape has changed in recent years. Since the 2019-20 school year, vaccination rates amongst school children – targeted for 95% – have fallen dramatically. According to KFF, a non-profit health policy organization, only11 US statesreported vaccination rates of 95% or higher in the 2023-24 school year. Previous vaccination recommendations took into account the fact that measles had been eradicated in the US, said Hazra. “All adults living in the US should be considered high-risk” right now, he says, and should receive two live doses at some point in their life, except for adults born before 1957.
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Dr David Nguyen, an internal medicine and pediatric infectious disease specialist at Rush University System for Health, has a similar take. “If an adult received only one MMR vaccine before the recommendation for two doses was made, they should consider getting a second dose.”
In the absence of a formal CDC guideline for all adults, one thing is clear: two live vaccines confer lifetime immunity. “There is also no value in getting more than two,” said Hazra. If you know you were vaccinated with the two doses of the live vaccine, he says, there is no recommendation for another dose, even in an outbreak or traveling internationally.
Last month,Robert F Kennedy Jr, the US health secretary, remarkedin an interviewthat immunity from the MMR vaccine “wanes 4.5% a year” and that “older people are essentially unvaccinated”.
“That is factually incorrect,” said Hazra. “If it was true, we would be seeing more measles in people with histories of vaccination.” Hazra stresses the importance of including older adults in the discussion about measles protection; they’re more vulnerable to possible complications from measles infections, which include pneumonia. But all the experts I spoke to warn against widespread misinformation about the measles vaccine. “Levels of antibodies against the measles virus may decline over time,” adds Bednarcdzyk. “But in the cases we’ve seen so far in 2025, only 3% of the cases had documented history of measles vaccine receipt.”
Bednarczyk cites “no big differences for adults compared to children” and that side effects usually clear up in a few days. “A lot of these live vaccines elicit a greater immune response for 24-48 hours,” adds Hazra. “The body is mounting an immune response and creating a lot of energy to do so.”
The most common side effects are fever, soreness and swelling at the site of the injection, headache, muscle aches, tiredness or a mild rash. “In some very rare cases,” said Bednarczyk, “there may be a short-term drop in blood platelet levels after vaccination, which can also happen if you are infected with measles virus.”
A person infected with measles spreads the disease to an average of 18 new cases in unvaccinated individuals, said Bednarczyk, making measles one of the most infectious diseases out there. (By comparison, individuals with seasonal influenza usually infect about two other people.) “Airborne pathogens hang around for two hours,” added Hazra. “It can infect so many people because of this.”
The MMR vaccination is significantly safer than acquiring natural immunity via infection. “Having the measles disease runs the risk of complications later on,” said Nguyen. These include subsequent measles infections from “immune amnesia” and serious complications from measles-related encephalitis.
Anyone who is unsure about their vaccination status should speak to their healthcare provider about an MMR or titer test. A high level of immunity across the US will help protect everyone.
Jean Iversenis a Chicago-based writer and developmental editor