At least 124 cases of measles have been reported in Texas since late January — marking the largest outbreak in the state in close to 30 years. The dozens of reported cases have mostly affected children,

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

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.