Does a third dose of mumps vaccine, given during an outbreak, reduce the likelihood of subsequent infection?

A third dose of the mumps vaccine, given during an outbreak, is associated with a reduced risk of subsequent infection. (LOE = 2c)

Cardemil CV, Dahl RM, James L, et al. Effectiveness of a third dose of MMR vaccine for mumps outbreak control. N Engl J Med 2017;377(10):947-956.  [PMID:28877026]

Cross-sectional

Government

Population-based

There have recently been a number of outbreaks of mumps on college campuses, despite more than 90% vaccine coverage with 2 doses of the mumps vaccine. From August 2015 through May 2016 such an outbreak occurred at the University of Iowa, ultimately causing 259 cases (attack rate 12.6 cases/1000 persons). Overalll, 98% of students had received 2 doses of the vaccine prior to the outbreak and the university held a series of mass vaccination events to provide a third vaccination. These researchers from the Centers of Disease Control found that the attack rate was lower if the second mumps dose had been given more recently, and was also lower for students who were given a third dose compared with those who'd received only 2 doses (6.7 vs 14.5 cases/1000 persons). A multivariate analysis confirmed these associations. Overall, at 28 days after the third dose, the hazard ratio for infection was 0.22 (95% CI 0.12 - 0.39). Of course, it is possible that students who chose to get the third vaccine also had better health habits.