During the prevaccine era, nearly everyone in the United States experienced mumps, and 90 percent of cases occurred among children who were 15 years of age and younger. During this time, it was estimated that 100,000 to 200,000 cases occurred in the United States each year. Since the mumps vaccine was licensed in 1967, this number has dropped dramatically. In 2003, fewer than 300 cases of mumps were reported.
You may wonder why people who have been vaccinated are getting sick. The reason is that the mumps vaccine (usually given as MMR -- the measles, mumps, and rubella vaccine) does not provide 100 percent protection. One dose of the mumps vaccine provides protection in approximately 80 percent of people, and two doses provide protection in approximately 90 percent of people. But even though the vaccine is effective, some of the cases of mumps in a mumps outbreak will be in people who were vaccinated against the disease. However, if the vaccine hadn't been used, the outbreak would have affected everyone, rather than just a small percentage of the population.
Anyone with mumps should not go back to childcare, school, or work for at least nine days after symptoms appear. People who come in contact with someone who has mumps should have their immunization status evaluated. Anyone who has not received mumps-containing vaccine (preferably MMR vaccine) should be vaccinated. The local health department or a physician can help determine if a person needs one or two doses of MMR vaccine. People who may have been exposed to the mumps virus should be educated on the signs and symptoms of mumps, and should seek medical attention if any of these symptoms appear.