Since 2006, a resurgence in mumps cases has prompted concerns over the effectiveness of the mumps vaccine and has thwarted the goal of eradication.
Mumps is a contagious viral infection causing fever and salivary gland swelling in children. If it is acquired after puberty, complications such as orchitis, or inflammation of the testicles, meningitis, and deafness may occur. Routine vaccination in Canada requires the first dose to be administered to babies between 12 and 15 months of age and a second dose to be administered at 18 months of age or later. The second vaccination must be received before school entry.
Is it declining immunity or poor effectiveness?
Since 2006, adults between the ages of 18 and 29 years old have experienced a resurgence in mumps infections. This was observed on university campuses in the US. These outbreaks have occurred in individuals with prior full immunization living in communities with high vaccination coverage. Two theories may explain the resurgence in mumps: waning immunity or vaccine ineffectiveness. Researchers at the Harvard T.H. Chan School of Public Health, in Boston, Massachusetts, in the US reviewed six epidemiological studies of mumps vaccine effectiveness to determine the cause of this resurgence. Their results were published in the journal Science Translational Medicine.
By using mathematical models of population data, the researchers tested the hypothesis of a declining immunity over time, which would suggest waning immunity, and the possibility of shifts in mumps virus genetics, which would suggest that current vaccinations are not as effective as they once were.
The results of the analysis allowed the researchers to determine the likely cause of the resurgence in mumps infestations is due to waning immunity. They estimate that current vaccines available today protect individuals from mumps infection for an average of 27 years. Over time, there has been a shift in the mumps virus genealogy; however, if the current vaccination protocols were ineffective, the resurgence of mumps infections would affect all children. The resurgence occurs among university-aged adults. This information demonstrates that despite a shift in the traits of the mumps virus, the vaccination guidelines are still effective. Nevertheless, mumps immunity declines over time.
A third vaccination may prevent mumps
The most effective measure of preventing the mumps is vaccination. The results from this study suggest the routine use of a third dose of a mumps vaccine to prevent resurgence. A policy of administering a mumps vaccine to US military recruits, regardless of their vaccine history, was implemented in 1991 and no resurgences in mumps cases have occurred among this population. In response to a university campus outbreak, protection against the virus was achieved when students were administered a third dose of a mumps vaccine. These two studies are observational in nature and based on limited evidence. Clinical trials studying the effectiveness and safety of an additional booster shot must be conducted before policies are changed. In addition, further studies are required to determine if immunity will wane after the third dose.
The expectation of eradicating the mumps through vaccination has been thwarted by recent outbreaks among young adults. The results of this study estimate that the current vaccination protocol for preventing the mumps is effective for an average of 27 years. Whether further doses are required later in the life of an adult is yet to be determined through further clinical trials.
Written by Jessica Caporuscio, PharmD
References:
(1) Lewnard JA, Grad YH. Vaccine waning and mumps re-emergence in the United States. Sci Transl Med. 2018.
(2) Tesini, BL. Mumps. Merck Manual Professional Version. 2018. https://www.merckmanuals.com/en-ca/professional/pediatrics/miscellaneous-viral-infections-in-infants-and-children/mumps
(3) Canadian Immunization Guideline. Part 4 – Active Vaccines: Mumps Vaccine. 2016. https://www.canada.ca/en/public-health/services/publications/healthy-living/canadian-immunization-guide-part-4-active-vaccines/page-14-mumps-vaccine.html#p4c13a8
