State health officials on Friday said the number of measles cases in the state linked to a West Texas outbreak has grown to 646 since January.

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

As more counties are being impacted by the ongoing measles outbreak and added to the growing list of counties across Texas, here's what to know.