The number of confirmed measles cases in western Texas grew to 146, and it is possibly spreading to the central part of the state and neighboring New Mexico, health officials said Friday.

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.

Health authorities warned of further spread. Most U.S. measles cases this year involved people 19 and under and those without a confirmed vaccination.