Mumps, once a ubiquitous childhood disease, was nearly eliminated in the United States after a vaccine came out in 1967. (It was folded into the three-part measles, mumps, rubella [MMR] vaccine in 1971.) But the disease is making a comeback, this time in young adults; there have been hundreds of outbreaks across U.S. college campuses since the early 2000s. Now, a new study reveals why: Protection from the mumps vaccine fades over time. A booster shot around age 18 could solve the problem, the researchers say. Read more.