Health officials sound alarms after Texas measles outbreak spreads to metropolitan area with nearly 100 sick now - Measles cases have also spread to neighboring New Mexico, sickening primarily childre

The largest measles outbreak in decades has reached San Antonio and San Marcos. Officials say an individual who tested positive for the virus in West Texas traveled to two major universities and one of the nation's busiest tourist attractions — the San Antonio River Walk.

Texas' measles outbreak is up to 90 cases. Here's what you need to know about the virus, vaccination and boosters.