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.

"I think that this is going to get into the hundreds of cases and could take many months to fully snuff out," Dr. Scott Gottlieb, the former commissioner of the FDA, said about the ongoing measles outbreak in Texas and New Mexico.

This is the tip of the iceberg,” said Rekha Lakshmanan, chief strategy officer for The Immunization Partnership in Houston, a nonprofit that advocates for vaccine access. “I think this is going to get a lot worse before it gets better.