Texas state health department data shows the vast majority of cases are among people younger than 18: 26 in kids younger than 4 and 51 in kids 5-17 years old. Ten adults have measles and three cases are “pending” an age determination. The Ector County Health Department told the Odessa American its case was in a child too young to be vaccinated.

Texas' measles outbreak is now at 90 cases, the highest yearly case count since 1992. Experts say the number is likely to grow more. Here's why.