Centers for Disease Control and Prevention (CDC) Director Tom Frieden on Sunday warned that the U.S. could see a "large outbreak" of measles.
"We are very concerned by the growing number of people who are susceptible to measles, and the possibility that we could have a large outbreak in this country as a result," Frieden said on CBS's "Face the Nation."
There are at least 102 reported cases in 14 states, according to the CDC. Frieden said that the U.S. is "likely to see more cases."
Frieden said there is "aggressive public health action" to identify those with measles, isolate those sick and quarantine those who have been exposed.
But he said the best way to prevent the spread of measles was vaccination.
Frieden said despite the U.S.'s 92 percent vaccination rate, there is growing evidence more parents are not vaccinating their children.
"What we’ve seen is, as over the last few years, a small but growing number of people, have not been vaccinated. That number is building up among young adults in society, and that makes us vulnerable," he said.
Frieden acknowledged that some parents are concerned about the safety of vaccines, or think measles no longer exists.
"One in six kids could have a fever ten days after, but the vaccine is safe and effective. And for those parents that may think that measles is gone, it’s still here, and it can be quite serious," he said.
Frieden also appeared on ABC's "This Week," urging parents to vaccinate their children.
"What you do for your own kids doesn't just affect your family. It affects other families as well," he said. "The more kids who are not vaccinated, the more they're at risk and the more they put their neighbors' kids at risk as well.”
--This report was updated at 2:40 p.m.