In a test of waning immunity after MMR vaccines, the majority of assays of serum samples from college students had detectable mumps immunoglobulin (Ig)G antibodies, but the magnitude was lower than that of rubella. The results of this study were published in the Proceedings of the National Academy of Sciences of the United States of America.
Blood samples were taken from 71 college students who were aged 18 to 23 years. These students were from non-outbreak areas and 80% had received their second MMR vaccine ≥10 years prior to this study. Samples were subjected to enzyme-linked immunosorbent assay to evaluate for antibodies and memory B cells (MBCs) to mumps, measles, and rubella.
Using IgG enzyme-linked immunosorbent assays, seroprevalence rates of mumps, measles, and rubella were determined to be 93%, 93%, and 100%, respectively. However, the concentration of IgG was significantly lower for mumps than for rubella according to the index standard ratio. In the sera of 59 participants who had sufficient IgG levels, high IgG avidity to the mumps Enders strain was also detected. Frequencies of circulating mumps-specific memory B cells were 5 to 10 times lower than for measles and rubella, and in 10% of participants, no detectable memory B cells to mumps were found. Further, geometric mean neutralizing antibody titers to mumps strain genotype G, the predominant circulation wild-type strain, were 6-fold lower than those against the Jeryl Lynn vaccine strain, genotype A.
This study was limited because of its cross-sectional nature and one-time sampling. The study authors also noted that for this study of waning immunity, the overall correlation between time from the receipt of last MMR vaccine and frequency of mumps-specific memory B cells was weak. However, they also concluded that, “the lower frequency of [memory B cells] in our college aged young adults supports weak long-term humoral immunity to mumps vaccine.” Therefore, further efforts to understand the factors associated with mumps immunity are recommended.
Investigators also stressed that despite these results, vaccination has led to a 99% reduction in the disease and that outbreaks are limited to areas with crowded living conditions, such as college campuses, where the force of infection can overwhelm lower herd immunity levels. Researchers recommended that strategies to improve the longevity and quality of humoral immune responses should be considered in the future.
Rasheed MAU, Hickman CJ, McGrew M, et al. Decreased humoral immunity to mumps in young adults immunized with MMR vaccine in childhood. Proc Natl Acad Sci USA. 2019;116:19071-19076.