An outbreak of measles has spread to 48 cases across four counties in the South Plains region of northwestern Texas, doubling in scope from earlier this week, health officials said. Most of the cases are in school-aged children,

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.

A rapidly growing measles outbreak in Gaines County, Texas, linked to low vaccination rates, has reached 48 cases, prompting urgent health warnings and vaccination efforts.