Researchers at the Centers for Disease Control and Prevention say about 90 percent of young-to-middle-aged Americans have antibodies against the mumps virus.
The CDC estimates between 90 and 92 percent of the population needs to be immunized in order to achieve what's known as "herd immunity," which prevents a large-scale outbreak of infection. They say the findings underscore the importance of giving children the recommended double dose of the measles-mumps-rubella vaccine.
