Third Times the Charm: Analyzing the Impact of a Third Dose of the Measles-Mumps-Rubella Vaccine in a University Mumps Outbreak

Abstract

Background: Mumps cases have recently been resurging within highly-vaccinated populations in the United States. This has prompted the Advisory Committee on Immunization Practices (ACIP) to recommend the use of a third dose of the Measles-Mumps-Rubella vaccine (MMR3) as a protective control measure during outbreaks. Although the use of MMR3 has recently been employed in several highly-vaccinated populations like universities, its effectiveness is not well resolved. This study attempts to quantify the impact of an MMR3 campaign on the spread of mumps during a university outbreak through transmission modeling.

Methods: A time-series Susceptible-Infected-Recovered model (TSIR) was designed using case incidence data, vaccination clinic data, and the mean generation interval of mumps to simulate the size of the outbreak with or without an MMR3 campaign. Additionally, the case data and mean generation interval were used to estimate the change in the effective reproductive number over the course of the observed outbreak and the simulated outbreak with no MMR3 campaign.

Results: The observed mumps outbreak with the MMR3 campaign saw about 75% fewer cases by the end of the academic calendar year than the simulated outbreak without the MMR3 campaign. The effective reproductive number decreased by nearly 82% over the course of the observed outbreak, and by about 68% in the simulated outbreak with no MMR3 campaign.

Conclusion: These findings indicate that an MMR3 campaign implemented during an outbreak can be effective at reducing the total number of mumps cases. A more robust understanding of mumps virus transmission in university settings and accurate understanding of the waning immunity of the second dose of MMR could improve the model and guide future public health policy.