A new study warns that the U.S. could see millions of new measles cases over the next 25 years if vaccination rates continue to fall. The research, published in science journal JAMA, used modeling to forecast the number of measles cases in several scenarios, including vaccination rates holding steady, rising or falling.

Measles could become endemic in the United States if routine childhood vaccination rates continue to decline, with up to 51 million illnesses over a 25-year period, according to a new study.

At current state-level vaccination rates, measles may become endemic again,” the authors wrote when they published their research this week in the Journal of the American Medical Association. Widespread vaccination against measles led to the virus being declared eradicated in the United States in 2000.