# Measles vaccines given long ago could be less effective now, doctors say

## As measles outbreaks continue, here’s how to know whether you need a booster

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Published March 2, 2025 1:44pm EST

### Dr. Marc Siegel explains measles outbreak spreading across the United States

Fox News senior medical analyst Dr. Marc Siegel joins 'Fox News Live' to discuss an outbreak of the measles virus in Texas and other areas of the United States.

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

Amid the current  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  for those who have not previously been infected or vaccinated, with up to a 90% chance of transmission.

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.



Some doctors are warning about the possibility of legacy vaccines becoming less effective over time. (iStock)

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  — about 97% effectiveness against measles."

**Who needs another vaccine?**
------------------------------

The question of whether someone should get another  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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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."



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. (iStock)

For those who are traveling to an area where a measles outbreak is occurring, he recommends that they  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.)



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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