The ongoing measles outbreak in West Texas has doubled in size to 48 cases, mostly in children and teens, making it the state's worst in nearly 30 years. State health officials said Friday in a news release that those who are infected are either unvaccinated or their vaccination status is unknown.

Nine of those infected were hospitalized and more cases are likely, health authorities said. U.S. vaccination rates for measles are falling, according to the CDC.