A measles outbreak in Texas has jumped from two cases among unvaccinated children to 48. With childhood vaccine hesitancy on the rise, outbreaks are increasingly likely.

The measles outbreak, which began spreading in late January, has caused several hospitalizations, with at least nine confirmed cases and three probable cases as early February. Health officials warn that at least one in five afflicted individuals will need to be hospitalized,

The measles outbreak in rural West Texas has grown to 58 cases as of Tuesday, and eight people in neighboring eastern New Mexico also have been diagnosed with measles. Public health officials in New Mexico have said they suspect some of the state’s cases are linked to the Texas outbreak, but haven’t confirmed it.