For those who were vaccinated for measles many decades ago, there’s a chance the protection has worn off by now.

Amid the current measles outbreak in West Texas — and with cases also reported in New Mexico, New Jersey and several other states — some doctors are warning about the possibility of legacy vaccines becoming less effective over time.

Measles is a highly contagious virus for those who have not previously been infected or vaccinated, with up to a 90% chance of transmission.

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The measles vaccine was first introduced in 1968. Three years later, in 1971, the MMR vaccine made its debut, providing a trifecta of protection against measles, mumps and rubella.

A couple of decades after the release of the MMR vaccine, measles was declared eliminated in the U.S. in 2000. 

“The standard recommendation from health authorities like the CDC is a two-dose series of the MMR vaccine,” Fox News medical contributor Dr. Nicole Saphier told Fox News Digital.

“For most people, these two doses provide lifelong immunity — about 97% effectiveness against measles.”

Who needs another vaccine?

The question of whether someone should get another measles vaccine depends on a few factors, like their vaccination history, age and health status, according to Saphier, who practices in New York.

“If you’re an adult who got both doses as a kid, you’re likely fine unless you’re in a high-risk group — such as healthcare workers or travelers to outbreak areas — where a booster might be considered,” she said.

“Adults who were vaccinated for measles between 1963 and 1968 should check their vaccination history.”

People born before 1957 presumably have natural immunity, as they were likely exposed to measles before vaccines became available, according to the doctor.

“Adults who were vaccinated for measles between 1963 and 1968 should check their vaccination history to determine which vaccine they received,” Saphier advised. 

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“During that time, a version of the vaccine that used an inactivated form of the virus was available that was found to be not as effective and was ultimately withdrawn.”

Studies show that antibody levels can wane over decades, but actual measles cases in fully vaccinated people remain rare, Saphier added.

“No hard data says people need a third shot routinely, but if you’re worried, a blood test can check your antibody levels,” she said.

“As with everything in medicine, there are rare risks to vaccinating and substantial risks to not vaccinating.” 

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Each person’s situation is different and should be weighed carefully after a thorough conversation with a trusted medical team, Saphier added.

Dr. Marc Siegel, clinical professor of medicine at NYU Langone Medical Center and a Fox News medical contributor, also emphasized the importance of measles vaccinations — “particularly with the number of circulating measles cases and underimmunized people coming into the U.S. at a time when there is a big measles surge around the world.”

For those who are traveling to an area where a measles outbreak is occurring, he recommends that they see a doctor for a measles “titer test” and get a booster if they are not showing immunity. (The titer test measures an individual’s level of immunity to the virus.)

“This is not yet an official suggestion anywhere, but I do check measles titers in many of my patients, and if they are low, I may give a booster as a precaution,” Siegel said.

MMR is a live virus vaccine and cannot be given to pregnant women or immunocompromised people, the doctor noted.

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So far in 2025, a total of 164 cases of measles have been reported in the U.S., according to data from the Centers for Disease Control and Prevention (CDC).

A vast majority of those (140) are in Texas. Nine cases have been reported in New Mexico, with the remainder in California, Georgia, Kentucky, New Jersey and Rhode Island.