U.S. Health Secretary Robert F. Kennedy Jr. said last week he would send Texas 2,000 doses of the measles, mumps and rubella vaccine through its immunization program. Kennedy founded the anti-vaccine group Children’s Health Defense, but has said he would not prevent Americans from getting vaccinated.

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