“What we call the community immunity or herd immunity threshold for measles is about 95 percent. So statewide we are falling short of that. So that does mean that Colorado is potentially at risk for outbreaks,” said the state epidemiologist, Rachel Herlihy.

Texas and New Mexico's health departments said on Friday measles cases in their states have risen to 444, an increase of 74 infections since their last reports three days ago, as the U.S. deals with one of the largest measles outbreaks in a decade.