A new study suggests that a third dose of the mumps vaccine may be helpful in combating waning immunity under the current schedule.
The study, published in March in Science Translational Medicine, analyzes the origins of a resurgence of mumps cases in vaccinated populations and suggests that it may be worth investigating whether a third dose of the vaccine is warranted for the general population.
The mumps vaccine was introduced in the 1960s, and recommendations were changed to add a second dose in 1989. A recommendation for a third dose in populations facing outbreaks was added in 2017, but this study suggests that may not be enough. In recent years, outbreaks of mumps in vaccinated populations—specifically among young adults on college campuses—had raised concerns over the efficacy of the current mumps vaccine. Researchers have questioned whether new strains or waning immunity is to blame, and this study indicates the latter may be most likely.
“The resurgence of mumps appears attributable to waning vaccine-induced immunity as opposed to a new strain of mumps virus,” says Yonatan Grad, MD, PhD, assistant professor of Immunology and Infectious Diseases at the Harvard T.H. Chan School of Public Health and co-author of the report. “Our analysis suggests that vaccine-induced protection wanes over time. The mechanisms that may be driving waning are really interesting and are not well understood.”
A third dose for waning immunity
The study’s findings were not related to the Advisory Committee on Immunization Practices’ (ACIP) October 2017 recommendation for a third dose of the mumps vaccine in the context of outbreaks.
The report offers an analysis of 6 epidemiologic studies about the efficacy of the mumps vaccine and found that roughly a quarter of everyone vaccinated in the United States could potentially lose protection from the vaccine within 8 years from immunization. Another 50% could lose protection within 20 years, and 75% within 40 years, the report notes. The research team didn’t find evidence of new strains contributing to outbreaks, but suggests waning immunity is a problem.
The research team suggests that additional studies should investigate whether a third general dose—not one that is given only in response to an outbreak—should be added to the mumps vaccine protocol.
“We found that protection afforded by 2 vaccine doses alone is unlikely to support elimination of endemic mumps virus transmission from the United States in the long term,” the study notes. “Although administering a third vaccine dose by 18 years of age would not necessarily confer lifelong protection based on our estimate of the time to loss of immunity, we nonetheless predict that this intervention could extend protection through young adulthood, thereby protecting age groups at risk in recent outbreaks.”
The study provides an example of where this policy is already in place—among new military recruits.
“Although congregated US military populations resemble high-risk groups based on their age distribution and close-contact environments, no outbreaks have been reported in the military since a policy of administering [a measles/mumps/rubella (MMR)] dose to incoming recruits, regardless of vaccination history, was adopted in 1991,” the study says. “In addition, receiving a third dose was associated with protection in a recent observational study after a third-dose campaign undertaken in response to a university campus outbreak, building on limited evidence from previous studies where third doses were only administered at the tail end of outbreaks.”
A booster for older adults
For older adults outside the typically high-risk population, researchers say a booster of the vaccine every 10 to 20 years may be beneficial.
“Whereas we estimated that most older adults are currently immune to mumps virus because of previous infection, our modeling suggested that neither a 2-dose nor a 3-dose vaccination program would be expected to protect more than 50% of adults beyond the age of 40 years in the long term. This concern may motivate the use of routine booster doses in adulthood. On the basis of our model, we expect that administering additional doses every 10 or 20 years would lead to sustained protection.”
Maintaining high immunity levels throughout the population, and not just in high-risk groups, may help prevent the emergency of new mumps virus strains, according to the study.
Grad says more research is needed before a general third dose of the mumps vaccine can be recommended, with studies specifically targeting how well the vaccine elicits protective immunity in young adults.
“Clinicians are often taught about mumps in its prevaccine epidemiology, in which peak incidence is in the 5- to 9-year-old age group,” Grad says. “However, with the recent outbreaks in the United States, the outbreaks are taking place in young adults. As such, clinicians should be aware that mumps may appear outside the traditional pediatric cohort and may also appear in individuals who have undergone mumps vaccination.”