More than 6,000 cases of mumps were reported in the United States last year, the highest number in 10 years. Around 2010, total annual cases were down in the hundreds. Most of the recent cases occurred in outbreaks, including a large one in Arkansas, rather than as a sporadic here-a-case, there-a-case disease. Most of the outbreaks were among people 18 to 22 years old, most of whom had had the requisite two doses of mumps vaccine in childhood. "We are seeing it in a young and highly vaccinated population," Dr. Routh said. Mumps is transmitted by droplets of saliva or mucus. It can be spread by coughing and sneezing, but also by sharing cups ... close contact. Many of the recent outbreaks occurred in college dorms or among athletic teams. Mumps vaccine is now combined with measles and rubella vaccine in the M.M.R., given at ages 1 and 4. But the immunity wanes over time in some people, and with close contact, there can be sufficient exposure to sufficient quantities of virus to overcome the vaccines' protection. Dr. Alan Lucerna [also] reported in February 2017 on a case of mumps in a fully immunized adult, in an article titled "Still a pain in the neck after all this time."