Harvard Study Links Mumps Outbreaks to Waning Vaccine Immunity

The recent spate of mumps outbreaks across the country, including one at Harvard, may be due to the waning effectiveness of the mumps vaccine, according to a new study published by two researchers at the Harvard School of Public Health.

Yonatan Grad, assistant professor of immunology and infectious diseases, joined Joseph Lewnard, a postdoctoral research fellow who is the study’s lead author, to publish their research in “Science Translational Medicine" this week.

The pair brought together data from six different research studies to draw their conclusions. In an interview Wednesday, Grad pointed to the 2016 mumps outbreak at Harvard—which affected more than 40 students—as an inspiration for the analysis.

“It was actually the Harvard outbreak that first caught my attention and then got me interested in explaining the question of why we’re seeing a resurgence of mumps in highly vaccinated populations,” he said.

Cases of mumps have been on the rise nationwide, according to the Centers for Disease Control and Prevention. In 2017, more than 5,000 people contracted the disease, up from fewer than 1,000 in 2012. College campuses have been hit particularly hard, which experts have previously attributed to the close contact between students.

Grad said he wanted to discover whether the increase in mumps cases was due to a new strain of mumps resistant to the vaccine—or due to the vaccine’s effectiveness wearing off as patients aged. Currently, federal recommendations call for two vaccinations: one between 12 and 15 months of age, and a second between four and six years.

“In our analysis, we saw that waning was consistent with what we were observing, whereas the appearance of a new strain that escaped the vaccine was not,” he said.

Lewnard added the concentration of recent mumps cases in young adults, who have not received vaccinations in years, suggests a decline over time in the vaccine’s preventative capacity.

“Without waning of protection, there’s not much reason why a strain should be focused in older age groups like young adults,” he said.

Harvard University Health Services Director Paul J. Barreira oversaw the University’s response to Harvard’s outbreak two years ago. During the outbreak, University Health Services placed almost a dozen students in isolation to prevent the spread of the disease.

Barreira said he worked with the authors of the study to compare the cost-effectiveness of isolating infected students versus vaccinating healthy students in order to manage mumps outbreaks.

While Barreira said declining vaccine immunity forms “the best explanation” for the Harvard outbreak, he also mentioned the vaccine is not 100 percent effective.

“Even if the vaccination was maximally protective, there would still be a 15 percent or so rate of developing the infection,” he said.

In the research paper, the authors suggest a third vaccination around age 18 as a possible means to reduce cases of mumps. The scientists are not the first to consider this idea: In light of recent research, the CDC recommended a third dose for at-risk populations in a January report.

Still, official recommendations do not call for all people to be routinely vaccinated at 18, which the authors say “should be assessed in clinical trials.”

—Staff writer Luke W. Vrotsos can be reached at luke.vrotsos@thecrimson.com. Follow him on Twitter at luke_vrotsos.