As measles cases continue to increase among unvaccinated individuals across the U.S., some Americans are questioning whether the measles vaccine they received as children is still effective. However, health experts say most people do not need to be concerned.

Dr. Donald Dumford with the Cleveland Clinic reassures the public that those who have been vaccinated remain protected. He notes that only a small group of individuals, specifically those who received a measles vaccine between 1963 and 1967 may need a booster, as that early version of the vaccine was found to be less effective.

“People that got vaccinated between 1963 and 1967, that vaccine is known to not be as effective,” Dr. Dumford explained.

While measles cases continue to rise in parts of the country, health officials emphasize that vaccinated individuals are at minimal risk. Among the more than 250 measles cases recently reported in Texas, only two involved vaccinated patients.

Measles cases have now been reported in Alaska, California, Florida, Georgia, Kansas, Kentucky, Maryland, Michigan, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, and Washington. The U.S. Centers for Disease Control and Prevention (CDC) defines an outbreak as three or more related cases, and so far in 2025, there have been three such clusters.

Measles is a highly contagious virus that initially infects the respiratory tract before spreading throughout the body. Symptoms include high fever, runny nose, cough, red and watery eyes, and a rash. The rash typically appears three to five days after the onset of symptoms, beginning as flat red spots on the face before spreading downward. As the rash develops, the fever can spike above 104°F, according to the CDC.

Health officials continue to urge vaccinations as the best defense against the virus.