A measles case has been confirmed in an unvaccinated adult who recently traveled internationally, according to Colorado health officials, the first measles case in the state in years as an outbreak of the highly contagious illness continues spreading in Texas and several other states.

A measles outbreak in Kansas doubled in less than a week to 23 cases and has “a possible link” to outbreaks in Texas and New Mexico that have sickened more than 370, the state health department said Wednesday.

Most of the public school districts in the Kansas counties experiencing the outbreak have vaccination rates well below the recommended 95% threshold.

Nine of the measles cases in Kansas are unvaccinated children, and the one other case is an under-vaccinated child with only one of two doses.