A growing measles outbreak in west Texas has infected 48 people, according to official state data released Thursday -- the latest sign that the once-vanquished childhood disease is making a comeback as vaccination rates decline.

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.

As of Tuesday, 22 children and two adults had been infected, all of whom were unvaccinated, local officials said.