The Centers for Disease Control and Prevention reported 800 confirmed cases of measles in the U.S. as of Friday, making the announcement as the highly contagious illness has reached half of the country—though most cases remain focused in Texas.

The Texas Department of State Health Services on Friday, reported 597 measles cases in the state since late January, an increase of 36 since the update on Tuesday. The department said the outbreak is primarily in West Texas and added that 4% or fewer than 30 of the confirmed cases are estimated to be actively infectious since their rash onset date was less than a week ago.