A measles outbreak in Texas has grown to 90 cases, mostly among unvaccinated children, state health data published Friday shows.

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.

Measles is a respiratory virus that can survive in the air for up to two hours. Up to 9 out of 10 people who are susceptible will get the virus if exposed, according to the U.S. Centers for Disease Control and Prevention.