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Usually delivered as part of the MMR (measles, mumps, rubella) vaccine.

What’s new: Experts are considering whether evidence warrants giving people a third dose of the MMR vaccine during an outbreak.

Why: In the past ten years or so, the majority of mumps cases were part of large outbreaks in densely populated places like college campuses, so scientists are studying how to help keep these eruptions under control. Last year alone there were more than 5,800 mumps cases—the most in a decade. The MMR vaccine is about 78 percent effective at preventing mumps with one dose and 88 percent effective with two; not much is known about the effect of a third. A recently formed mumps work group is expected to make recommendations by February 2018.