The measles outbreak centered in the South Plains region of Texas grew to 541 cases across the state on Friday, according to health officials. The Texas Department of State Health Services reported that 56 have been hospitalized for treatment since the outbreak began in late January.

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.