The Centers for Disease Control and Prevention confirmed nearly 900 measles cases in the U.S. on Friday, though much of the measles cases in the country remain centered in Texas, which confirmed earlier this week there have been 624 cases of the highly contagious illness in the state this year.

The U.S. declared measles eliminated 25 years ago. But the growing outbreak of the disease centered in West Texas poses a threat to this coveted status—and signals the possibility of measles becoming more common.