Texas is in the midst of the worst measles outbreak in decades, with 90 cases across 7 counties. Here’s what to know.

According to the CDC, if you were born after 1957, one dose is considered sufficient to be considered protected from measles. Some adults may need a second dose. The CDC says adults who are going to be in high-risk settings for transmission should make sure they’ve had two doses at least 28 days apart.

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