Third MMR Dose May Cull Future Mumps / Measles Outbreaks

A third dose of the measles-mumps-rubella (MMR) vaccine may help control a mumps outbreak propagated waning immunity within the affected population, a new study has concluded.

In the study, published on September 7, 2017 by the New England Journal of Medicine (NEJM), researchers from the Centers for Disease Control and Prevention (CDC), the Iowa Department of Public Health, the Johnson County (Iowa) Department of Public Health, and the University of Iowa documented the impact of a large MMR vaccine campaign initiated during a mumps outbreak at the Iowa City school during the 2015-2016 academic year. Of the more than 20,000 students enrolled at the time, 259 were diagnosed with mumps by the end of the outbreak.

The authors of the NEJM study believe the results would have been much worse without their intervention. After reviewing the health records of all of the university students, they found that 98.1% had received at least 2 doses of MMR vaccine prior to the outbreak. However, they also identified a notable trend: The more time that had elapsed between the time they received the first dose and the second dose of the vaccine, the greater their risk of contracting mumps. Those students who had received their second shot ≥13 years prior to the outbreak were 9 times more likely to be diagnosed with mumps than those who had been vaccinated more recently.

In response to the mumps outbreak on campus, which started in the fall of 2015, University of Iowa officials required all students enrolling for the spring semester to receive at least 2 doses of the MMR vaccine prior to registering. In addition, working with local public health officials, the university launched a vaccination campaign that included 8 free vaccine clinic days on campus; in all, 4783 of the students received a third dose of the MMR vaccine during these clinics. Among those who received the third dose, the authors of the NEJM study authors found that the incidence of mumps was lower (6.7 cases per 1000 population) than it was among students who received only 2 doses (14.5 cases per 1000 population). Overall, receipt of a third MMR vaccine dose was associated with a 78% lower risk of mumps than receipt of a second dose (4 weeks after vaccination), the study authors noted.

In their concluding remarks, they note, “These findings suggest that the extent of the outbreak was limited by routine vaccination and by a strict university requirement that all students receive 2 doses of MMR vaccine, although waning immunity probably contributed to the propagation of the outbreak.”

In light of the small, but vocal opposition to the MMR vaccine, the authors of the NEJM study hope that their findings will inform management approaches in university settings and elsewhere. “The Advisory Committee on Immunization Practices is currently looking at the mumps vaccine and future recommendations,” study co-author Patricia Quinlisk, MD, MPH, Medical Director/State Epidemiologist, Iowa Department of Public Health told Contagion^®, “and college campuses experiencing outbreaks often look to CDC or states that have had previous outbreaks for guidance.”

Brian P. Dunleavy is a medical writer and editor based in New York. His work has appeared in numerous healthcare-related publications. He is the former editor of Infectious Disease Special Edition.