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.

A fast-growing measles outbreak in West Texas has nearly doubled in just one week, now totaling 90 cases across seven counties and spreading to New Mexico. Earlier this week, the Texas Department of State Health Services confirmed 49 cases in five counties.

Texas reported 90 cases this week, while New Mexico reported nine. A majority of the cases have been in a Texas county where vaccination rates have lagged behind the rest of the state.