As annual cases of mumps in the United States climb, it has been suggested that waning vaccine-induced immunity
may be to blame.
Now, a new study conducted by investigators from Emory Vaccine Center and the US Centers for Disease Control and Prevention (CDC) demonstrated insufficient immunity in a fraction of college-aged individuals who were vaccinated against mumps in childhood. Results of the research were published in the Proceedings of the National Academy of Sciences
“Overall, the MMR [measles, mumps, rubella] vaccine has been great, with a 99% reduction in measles, mumps, and rubella disease and a significant reduction in associated complications since its introduction," Sri Edupuganti, MD, MPH, associate professor of medicine (infectious diseases) at Emory University School of Medicine and medical director of the Hope Clinic of Emory Vaccine Center, said in a press release
According to Edupuganti, there are 2 possible reasons for a rise in the number of outbreaks occurring among college students, sports teams, and close-knit communities.
"What we're seeing now with these mumps outbreaks is a combination of 2 things—a few people were not making a strong immune response to begin with, and the circulating strain has drifted away from the strain that is in the vaccine," he said.
The study enrolled 71 individuals aged 18 to 23 years living in the Atlanta, Georiga, area. According to the investigators, this was the largest study to date that examined mumps memory B cells among vaccinated individuals.
Of the 71 individuals enrolled in the study, 29 participants had received 2 doses of the MMR vaccine. However, 80% of the participants received their second dose more than 10 years prior to enrollment of the study in 2010.
The vast majority (93%) of participants had antibodies against mumps, but 10% of participants had no detectable mumps-specific memory B cells. These cells are normally capable of producing antiviral antibodies as memory response following an exposure to mumps virus.
In comparison, the average frequency of memory B cells making antibodies against mumps among participants was 5 to 10 times lower than cells making antibodies against measles or rubella.
Furthermore, the investigators noted that antibodies from the participants were not as effective at neutralizing wild-type mumps virus when compared with the vaccine virus. In this study, at least 6 individuals may have been susceptible to infection with the currently circulating wild-type strain.
It is important to note that the investigators did not see a clear association between the timing of vaccination and low antibody or memory B cell levels.
Previous research has demonstrated that a third dose of the MMR vaccine
could increase neutralizing antibody responses to mumps in some individuals, but the effects have not been shown to be long lasting.
The Jeryl Lynn mumps vaccine strain that is in the MMR vaccine was cultured in the 1960s and, although there is 1 serotype of mumps virus, the currently circulating strain genotype G is genetically distinct from the vaccine strain. Currently, it is unknown how genetic changes influence the antigenic properties of the currently circulating strain.
Additional studies are needed to characterize the immune response to currently circulating and vaccine strains of mumps are clearly needed to determine if it is necessary to develop a new mumps vaccine, the study authors conclude.
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