Before the measles vaccine was introduced in 1963, the disease caused major epidemics every two to three years—and 2.6 million deaths worldwide each year. But by 2000, measles was considered “eliminated” in the United States, thanks primarily to vaccination efforts.
Eliminated is a term that means a disease was not continuously transmitted for more than a year in a specific geographic area. Another term—eradicated—means a disease has been eliminated worldwide. For example, polio was eliminated from the U.S. in 1979, but still exists in other places around the world. Smallpox, however, was eradicated globally in 1980.
But if measles was eliminated in 2000 in the U.S., why are there reports of new cases now?
Basically, if a disease is eliminated, outbreaks (defined as three or more cases) can still happen if someone who is unvaccinated travels to a country where the disease is still common and becomes infected. Once back at home in the U.S., that traveler can transmit measles to anyone who is unvaccinated.
In 2024, the World Health Organization (WHO) estimated there were 11 million measles cases and about 95,000 deaths worldwide, with cases in the WHO European region up 47% compared with 2019.
Here in the U.S., the Centers for Disease Control and Prevention (CDC) has reported 39 outbreaks and 3,471 confirmed cases as of mid-September—the highest annual count since 1991 and already more than in all of 2025, when 2,289 cases were reported. Pennsylvania officials have attributed four deaths in the state to measles complications this year. The CDC has not included those deaths in its national count. Most of the reported cases have been in people who were unvaccinated or whose vaccination status was unknown.
An independent commission of public health experts will review in November whether the U.S. still meets the standard for elimination.
“This is a serious, highly contagious viral disease and the only strategy we have to fight it is vaccination. And that is a strategy that has worked very well for many, many years,” says Marietta Vázquez, MD, a Yale Medicine pediatric infectious diseases specialist and vaccine expert. “If people are saying no to this vaccine, we need to consider what their reasons are and if they have the information they need.”
