The Centers for Disease Control and Prevention (CDC) and the White House urged individuals and parents to vaccinate themselves and their children amidst an outbreak of at least 100 measles cases originating at Disney theme parks in December. The virus was declared eliminated in the U.S. in 2000.

"[From] what we've seen as over the last few years, there is a small but growing number of people [that] have not been vaccinated,” Dr. Thomas Frieden, Director of the CDC told CBS on Sunday. “That number is building up among young adults and adults in society. And, that makes us vulnerable. We have to make sure measles doesn't get a foothold in the U.S."

The White House on Friday urged parents to heed the advice of public health officials and scientists in getting their children vaccinated.

"People should evaluate this for themselves with a bias toward good science and toward the advice of our public health professionals," President Barack Obama's spokesman Josh Earnest told reporters.

The measles outbreak has renewed a debate over the so-called anti-vaccination movement. A small minority of parents have refused to allow their children to be inoculated over fears that vaccines may have side effects— one being autism. But research that proves a link between autism and the measles vaccine has not born out, the CDC says.

More On This...

Frieden said most of the parents of unvaccinated children don’t have strong feelings on the issue.

“They’re just concerned that maybe measles isn’t around anymore or maybe their kid shouldn’t get one more shot,” he told ABC.

Unvaccinated children put others at risk, including children who can’t be vaccinated and those who have immune problems, he added.

“What you do for your own kids doesn’t just affect your family— it affects other families as well,” he told ABC.

The CDC has confirmed 100 measles cases in the U.S so far this year, and most of them linked to an outbreak that began in Disneyland in December, public officials said Friday. According to the California Department of Public Health, at least 58 of the cases of the highly infectious disease in the state have been epidemiologically linked to the Disneyland cluster. More than a dozen other cases have been confirmed in 13 other U.S. states and in Mexico.

No deaths have been reported in connection with the outbreak, which public health officials suspect began when an infected person from outside the U.S. visited Disneyland in Anaheim between Dec. 15 and Dec. 20.

Measles was officially declared eliminated in the United States in 2000 after decades of intensive childhood vaccine efforts. But last year the nation had its highest number of measles cases in two decades. The CDC reported more than 600 measles cases that year.

Reuters, the International Business Times, and the Wall Street Journal contributed to this report.