In 2000, the U.S. declared that widespread vaccination efforts had successfully eliminated measles — a highly contagious viral infection — from the country. After that, the disease affected only a relatively small population, mostly made up of people who traveled internationally, and it remained confined.
But since the beginning of this year, at least 764 cases of measles have been confirmed across 23 states, according to the U.S. Centers for Disease Control and Prevention (CDC). It’s the biggest outbreak in 25 years.
