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According to the manufacturer’s product insert, the mumps vaccine is 96 percent effective. However, the Centers for Disease Control (CDC) reports that two doses of mumps vaccine are between 31 and 95 percent effective, while a single dose is 49 to 91 percent effective.
Mumps outbreaks in highly vaccinated populations began in 2006 with the majority of cases occurring among young adults between the ages of 18 and 24. By the late 2000s, researchers began speculating that the lack of natural boosting from exposure to wild-type mumps may be resulting in waning of vaccine acquired immunity. Moreover, the number of asymptomatic patients transmitting the infection to others may be higher than the estimated 30 percent, thus affecting public health measures designed to contain the outbreak. As a result of the resurgence in mumps cases among highly vaccinated individuals, experts reported that measures to locate unvaccinated individuals would not be helpful, as they were not considered to be responsible for mumps outbreaks. A third dose of mumps vaccine (MMR) was suggested as method of preventing and containing further outbreaks.
Studies have noted mumps vaccine waning as evidenced by outbreaks occurring more frequently among adults, rather than children, with researchers predicting an increase in mumps outbreaks as the temporary vaccine-induced immunity replaces longer lasting natural immunity to the disease. The time between the last dose of mumps vaccine (MMR) and the onset of the disease appears to be a factor in outbreaks, suggestive of vaccine waning and its inability to confer long lasting immunity.
Several researchers have reported the current two-dose MMR vaccine strategy to be ineffective at preventing mumps outbreaks. Additionally, while health officials believe that the administration of a third dose of MMR vaccine may assist in controlling an outbreak, they have also indicated that routine recommendation of an additional dose will not prevent mumps outbreaks. Both the rapid decrease in vaccine induced mumps antibody levels, as well as the emergence of mumps strains not targeted by the vaccine, may cause additional booster doses of mumps vaccine to be ineffective at preventing and controlling mumps outbreaks. The limited effectiveness of the current vaccine strategies to prevent mumps outbreaks has prompted several experts to recommend that more research be dedicated to examining the immune system’s response to mumps vaccination. Numerous studies focused on the continued mumps outbreaks occurring in highly vaccinated populations have many researchers suggesting that both the waning of vaccine induced immunity and the lack of an effective mumps vaccine may be to blame.
The MMRII and ProQuad (MMRV) vaccines contain mumps genotype A, the Jeryl Lynn strain, isolated from samples collected in 1963. However, since 2006, mumps genotype G has become the predominant circulating strain of mumps in the United States. The CDC reports that while studies have found the Jeryl Lynn (genotype A) strain effective at preventing mumps infections caused by genotype G, vaccine induced antibodies have been noted to be lower. In 2015-2016, a large mumps outbreak involving mumps genotype G in Norway concluded that the genotype A found in the MMR vaccine offered “suboptimal protection against mumps genotype G”. Additional studies have also reported that the Jeryl Lynn mumps strain to be inadequate to protect against the strains of mumps that are currently circulating.
In 2010, two former Merck employees filed a lawsuit alleging that Merck altered the vaccine efficacy testing and study results in an attempt to make the mumps vaccine appear more effective than it is. Specifically, the lawsuit made claims that mumps outbreaks in vaccinated individuals were directly related to the alleged falsification of efficacy data. As of December 4, 2022, the lawsuit was still pending.
In October of 2017, as a result of continual mumps outbreaks in highly vaccinated populations, the CDC’s Advisory Committee on Immunization Practices (ACIP) recommended a third dose of mumps vaccine (MMR) to be administered in the event of an outbreak. At the time of this recommendation, the use of a third MMR vaccine was reported to be between 61 and 88 percent effective at preventing mumps infection.
In June 2022, the FDA and CDC approved use of PRIORIX, a live attenuated measles, mumps, and rubella vaccine, for individuals 12 months of age and old. The effectiveness of PRIORIX was based on antibody responses when compared to the MMRII vaccine and according to the package insert, PRIORIX was considered non-inferior to Merck’s MMRII vaccine.
IMPORTANT NOTE: NVIC encourages you to become fully informed about Mumps and the Mumps vaccine by reading all sections in the Table of Contents, which contain many links and resources such as the manufacturer product information inserts, and to speak with one or more trusted health care professionals before making a vaccination decision for yourself or your child. This information is for educational purposes only and is not intended as medical advice.