The U.S. declared measles eliminated in 2000 "thanks to a very high percentage of people receiving the safe and effective measles, mumps, and rubella vaccine," the CDC said, but now U.S. coverage among children of kindergarten age is below the 95 percent coverage target, which creates a higher risk for outbreaks of the virus.

Some private schools have shut down because of a rapidly escalating measles outbreak in West Texas. Local health departments are overstretched, pausing other important work as they race to limit the spread of this highly contagious virus.