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.

The Texas health department reported 663 cases of measles in the state on Tuesday, an increase of 17 cases since April 25, as the U.S. battles one of its worst outbreaks of the childhood disease. Cases in Gaines County,

Texas health officials reported 17 new measles cases on April 29, bringing the total confirmed cases since late January to 663.