Outbreaks and Findings

In 2006, there was a mumps outbreak that started at an Iowa university, then spread to other Midwestern states. In one month, there were more than 1,600 cases reported and by the time the outbreak had run its course, more than 6,000 people had been stricken with mumps. Researchers studying the outbreak have come up with several important findings.

The relatively low vaccination rate among Iowa youth was a contributing factor along with close contact in quarters such as dorms, classrooms and cafeterias. Because mumps is rarely in the news, vaccination rates have been falling. There are 15 states with vaccination rates lower than 90 percent. This, say experts, is an outbreak waiting to happen.

Another issue, this time with the vaccine itself, is also thought to be a contributing element. Experts believe the mumps vaccine wears off over time, with a resulting loss of efficacy. U.S. News reports that the mumps portion of the three-virus vaccine commonly used in the U.S., MMR, is less effective than the measles and rubella vaccines.

Dr. Paul Offit, director of the Vaccine Education Center at The Children’s Hospital of Philadelphia, says the mumps portion of the vaccine also becomes less effective after about ten years. "We’ve never eliminated mumps," he says. "It doesn’t induce as long-lasting of a response as measles and rubella." Officials consider measles and rubella eradicated from this country.

Research has revealed that measles immunity decreases in older persons. That could be due to the vaccine’s waning immunity. It could also point to genetic mutations in the wild mumps virus which renders the vaccine less effective. A study revealed that the mumps vaccine had a lower rate of efficacy when the attacking mumps virus possibly had mutational differences. More research is needed into this problem.