The measles outbreak in rural West Texas has grown to 58 cases as of Tuesday, and eight people in neighboring eastern New Mexico also have been diagnosed with measles. Public health officials in New Mexico have said they suspect some of the state’s cases are linked to the Texas outbreak, but haven’t confirmed it.

Measles is spreading across the U.S., with an outbreak growing in Texas and cases reported in nearby states. Experts explain whether or not you should be concerned.