New Mexico health officials announced that the measles outbreak has reached a third county in the state’s southeastern corner Tuesday.

Measles is caused by a highly contagious virus that’s airborne and spreads easily when an infected person breathes, sneezes or coughs. It is preventable through vaccines, and has been considered eliminated from the U.S. since 2000.

An unvaccinated child in Chaves County, NM has been diagnosed with measles, marking the third county in New Mexico affected by the ongoing outbreak.