In certain scenarios a third dose of the measles-mumps-rubella (MMR) vaccine may be considered a control measure against mumps, when transmission is sustained despite high 2-dose MMR coverage, say the Centers for Disease Control and Prevention (CDC).

The direction comes in a new statement from the CDC which details a mumps outbreak at the University of Illinois at Urbana-Champaign, in which 317 individuals had confirmed or probable mumps between April 2015 and May 2016. The median age of those infected was 20 years old.

The Illinois Department of Public Health (IDPH), the Champaign-Urbana Public Health District (C-UPHD), and the universities health center recommended all studies and staff members born in 1957 or after to receive an additional MMR vaccine dose. 

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The target for the recommendation was approximately 50,000 students and staff, 8,200 individuals received the third dose during August 6–27, and an additional 3,300 received it in the following fall and spring months.

The CDC have no recognized recommendations concerning a third MMR dose, however the agency has given guidelines for public health centers considering an additional vaccine during mumps outbreaks. CDC criteria for a third vaccine comprise of the following: intense exposure settings such as universities, evidence of sustained transmission for >2 weeks despite a high 2-dose coverage, high attack rates of >5 cases per 1,000 population, and in instances where traditional control measures fail.

The vaccine’s effectiveness has been estimated at 78% for the first vaccine dose and 88% for the second dose, although the effectiveness of the third dose is unknown. In previous outbreaks, a third dose intervention correlated with a decline in mumps rates (Pediatrics 2012;130:e1567–74 and Pediatr Infect Dis J 2013;32:374–80).

The disadvantages of administering a third dose can be unnecessary costs (as its efficacy has yet to be proved) and possible adverse events. The CDC states that they are, “gathering additional data to assess use of a third dose of vaccine to inform decision-making during outbreak responses and potential changes in the recommendations.”

In the case of the University of Illinois, transmission rates began to decline after August 2015, when the third dose was recommended as a control measure. The CDC says further evaluation is needed to determine whether this was a result of the third vaccination or not.

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