Health experts say low vaccination rates are fueling outbreaks of the contagious disease that was considered to be eliminated 25 years ago.
Health authorities warned of further spread. Most U.S. measles cases this year involved people 19 and under and those without a confirmed vaccination.
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.
A measles outbreak in Texas has reached San Antonio, with 90 cases reported, mostly in children. Vaccination remains crucial to control the spread.