The measles outbreak centered in the South Plains region of Texas grew to 663 cases on Tuesday, according to health officials. The latest update from the Texas Department of State Health Services adds 17 new cases since the agency's last update on Friday.

The Centers for Disease Control and Prevention confirmed nearly 900 measles cases in the U.S. on Friday, though much of the measles cases in the country remain centered in Texas, which confirmed earlier this week there have been 624 cases of the highly contagious illness in the state this year.

Among the 646 measles cases in West Texas, state health officials said 618 involved individuals who were either unvaccinated or had an unknown vaccination status. The CDC recommends two doses of measles, mumps and rubella vaccine for children 6 and younger and one or two doses for those who are older and don’t have evidence of immunity.