Public health authorities said Tuesday that an outbreak of measles in western Texas has expanded, while a new case was confirmed nearby across state lines in New Mexico

Two dozen cases of measles have been reported in a small West Texas county that has one of the state’s highest vaccine exemption rates. In Gaines County, which has a population of about 22,000, 24 cases of the airborne infectious disease have been reported since late January. Most of them are unvaccinated, school-aged children.

A small county in West Texas has 15 measles cases, mostly in school-aged children. Gaines County, which borders New Mexico, has one of the highest rates of vaccine exemptions in the state.