Recent Mumps Outbreaks

April 25, 2006

How many cases of mumps usually occur in the US each year?

In the United States , since 2001, an average of 265 mumps cases (range: 231-293) have been reported each year. (See related MMWR article: MMWR Dispatch-Mumps Epidemic-Iowa, 2006 (.pdf) March 30, 2006 [55(13);366-368] )

When did the outbreak in the Midwest start?

The first cases of mumps-like illness were reported from Iowa in December 2005. More cases have been occurring since then in Iowa, and in several other states.

Where did the outbreak in the Midwest start?

The current information indicates that the outbreak may have begun on a college campus. Colleges that have group living, dining, studying, and sports are areas that make disease transmission more likely, and increase the chance of outbreaks. Once started, such outbreaks sometime spread to the community, causing illness in persons who do not attend college. For this reason, CDC recommends that all college students have two doses of measles-mumps-rubella (MMR) vaccine. Studies have suggested that strict enforcement of these recommendations is important for preventing and stopping outbreaks.

Why are people who have been vaccinated getting sick?

One dose of mumps vaccine prevents approximately about 80% of mumps and two doses approximately about 90% of cases. Even though the vaccine is effective, if most persons in a population are vaccinated, most cases in an outbreak would also be expected to be vaccinated. However, if the vaccine hadn't been used, the outbreak would have affected everyone, rather than a small percent of the population.

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