At least 124 cases have been reported since late January, mostly among children and teenagers who were unvaccinated or whose vaccination status was unknown.

Here’s what to know about the outbreak after the first U.S. death since 2015 from the highly contagious—but preventable—respiratory disease.

The news on Wednesday that a child died from measles at a Lubbock hospital is something that infectious disease experts like Dr. Peter Hotez have feared since an outbreak of the virus began spreading in northwest Texas.