Mumps Outbreaks: Use Third Dose of Vaccine to Lower Risk

A third dose of the measles-mumps-rubella (MMR) vaccine had improved outbreak control at the University of Iowa during a mumps outbreak in the 2015-2016 academic year, according to a recent study.

Using Fisher’s exact test, the researchers compared the unadjusted attack rates of mumps based on dose status and years since the students had received a second MMR vaccine dose. The effectiveness of the vaccine was evaluated using multivariable time-dependent Cox regression models that adjusted for the number of years since the second dose. 
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Of the total 20,496 students who were enrolled at the university during the 2015-2016 school year, 98.1% had received at least 2 doses of the MMR vaccine, and 259 were diagnosed with mumps. During the outbreak, 4783 students had received a third MMR vaccine dose. 

The researchers found that the attack rate was lower among students who had received a third dose (6.7 cases per 1000) compared with those who had received only 2 doses (14.5 cases vs 1000). After 28 days, the third MMR vaccine dose was associated with a 78.1% lower risk of mumps compared with the second dose.

In addition, the effectiveness of 2 doses of the MMR vaccine was lower for students who had a distant receipt of the second dose compared with those who did not receive the vaccine. Students who had received a second MMR vaccine dose 13 years or more before the outbreak had a 9-fold increased risk for mumps.

“These findings suggest that the campaign to administer a third dose of MMR vaccine improved mumps outbreak control and that waning immunity probably contributed to propagation of the outbreak,” the researchers concluded.

—Melissa Weiss

Reference:

Cardemil CV, Dahl RM, James L, et al. Effectiveness of a third dose of MMR vaccine for mumps outbreak control [published online September 7, 2017]. N Engl J Med. doi:10.1056/NEJMoa1703309.