The U.S. is dealing with a big outbreak of the mumps.
As of mid-November, there have been more than 2,900 cases.
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Arkansas had 1,900, and Iowa has nearly 700.
A number of clusters are on college campuses, where close quarters help the virus spread faster.
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Many students may also be losing immunity from their childhood vaccinations.
The outbreak is so serious, the CDC is considering recommending a third dose of the mumps vaccine.