US Mumps Outbreak of 2016 Will Go Down as Largest in a Decade

As the year draws to a close, the mumps outbreak of 2016 will go down as the largest in the United States in a decade, as communities across the country continue to report new cases.

According to the Centers for Disease Control and Prevention’s (CDC) Morbidity and Mortality Weekly Report (MMWR), the United States has now seen at least 4,619 reported cases of the mumps this year. At this time in 2015 there were 1,216 reported mumps cases around the country, just slightly higher than the total for 2014, making this year’s outbreak nearly four times the size. The last time the United States experienced a larger outbreak was in 2006, when a number of Midwestern college campuses experienced outbreaks and the total number of cases topped 6,500.

While a number of states have reported little to no mumps cases so far this year, as of December 3, seven states in the Northeast and Midwest had reported 100 cases or more. Arkansas, Iowa, Indiana, Illinois, Massachusetts, New York, and Oklahoma have all been hardest hit in the current outbreak while Vermont, Delaware, Louisiana, and Wyoming have reported no mumps cases. Officials at the Arkansas Department of Health have reported 2,270 suspected cases so far in 2016, the most of any state in the current outbreak. They note that of those infected so far in Arkansas, 90% to 95% of school-aged children and 30% to 40% of adults were fully immunized with the measles, mumps, and rubella (MMR) vaccine. The CDC notes that two doses of the vaccine are 88% effective against the mumps, while one dose of vaccine is 78% effective. Although outbreaks of the mumps can still occur in populations with high vaccination rates, the vaccine prevents larger outbreaks and is associated with a lower rate of severe symptoms.

“If it were not for the vaccine,” note Arkansas Department of Health officials, “we would be seeing many, many more cases of the mumps. Also, we have only seen a few cases with complications, like swelling of the brain or testicles. Normally, we would expect to see many more persons with complications. This tells us that even though some vaccinated individuals are still getting the mumps, they are experiencing mild disease. The vaccine remains the best protection we have against the mumps.”

According to the MMWR report, after Arkansas, the worst hit states this year are Iowa with 657 cases, Oklahoma with 334 cases, Illinois with 317 cases, Massachusetts with 246 cases, Indiana with 235 cases, and New York, which has reported 151 cases upstate and 137 cases in New York City. Outbreaks can be more likely to occur on college campus, where students can have prolonged and close contact in dormitories, on sports teams, in classrooms, and through activities with Greek organizations. Colleges affected by the outbreak this year, including the University of Missouri and the State University of New York’s New Paltz campus, have offered MMR booster shots and free vaccine clinics to their students to prevent further spread of the mumps across their campuses.

With winter breaks now in effect for universities around the country, school officials at the University of Missouri and note that they will continue to monitor case reports, while the break will offer a reprieve from new transmissions on campus.