Several outbreaks of mumps, another viral disease for which there is no cure, have popped up in recent years. Most of the cases have occurred in areas where people are in close contact: summer camps, college campuses, Orthodox Jewish communities.
Some of those who caught the disease were left deaf, one of the possible outcomes of the disease, Offit said. But because people rarely see the consequences of these diseases anymore, many are no longer afraid of them.
"People don't fear the disease," Offit said. "When the diseases start to come back, people are more likely to respond to their fears. We're hard-wired for fear."
Despite the risks from the actual diseases, fears have shifted to the vaccines.
"When they don't see the disease, the mental calculus shifts to concerns about the vaccine and not the disease," Omer said.