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.

Measles would likely be the first eradicated disease to return, because it is so highly contagious, but other diseases like rubella, diphtheria and polio could also return if vaccination rates fall by half, according to the models.

Measles could be well positioned for a comeback in the United States in a very short period of time. If immunization rates continue to drop for a prolonged period of time, the US could see millions of measles cases over the next 25 years.