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.

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.

Health officials expect a measles outbreak in West Texas to exceed 100 cases because of low vaccine rates and undetected infections. Vaccine misinformation and new laws may make such situations more common and harder to contain.