Mumps Outbreaks in Vaccinated Populations—Is It Time to Re-assess the Clinical Efficacy of Vaccines?

Abstract

History illustrates the remarkable public health impact of mass vaccination, by dramatically improving life expectancy and reducing the burden of infectious diseases and co-morbidities worldwide. It has been perceived that if an individual adhered to the MMR vaccine schedule that immunity to mumps virus (MuV) would be lifelong. Recent mumps outbreaks in individuals who had received two doses of the Measles Mumps Rubella (MMR) vaccine has challenged the efficacy of the MMR vaccine. However, clinical symptoms, complications, viral shedding and transmission associated with mumps infection has been shown to be reduced in vaccinated individuals, demonstrating a benefit of this vaccine. Therefore, the question of what constitutes a good mumps vaccine and how its impact is assessed in this modern era remains to be addressed. Epidemiology of the individuals most affected by the outbreaks (predominantly young adults) and variance in the circulating MuV genotype have been well-described alluding to a collection of influences such as vaccine hesitancy, heterogeneous vaccine uptake, primary, and/or secondary vaccine failures. This review aims to discuss in detail the interplay of factors thought to be contributing to the current mumps outbreaks seen in highly vaccinated populations. In addition, how mumps diagnoses has progressed and impacted the understanding of mumps infection since a mumps vaccine was first developed, the limitations of current laboratory tests in confirming protection in vaccinated individuals and how vaccine effectiveness is quantified are also considered. By highlighting knowledge gaps within this area, this state-of-the-art review proposes a change of perspective regarding the impact of a vaccine in a highly vaccinated population from a clinical, diagnostic and public perspective, highlighting a need for a paradigm shift on what is considered vaccine immunity.

Introduction of Two-Dose Mumps-Containing Vaccine into Routine Immunization Schedule in Quzhou, China, Using Cox-Proportional Hazard Model

“…Recent mumps outbreaks in individuals who had received two doses of MMR vaccine have challenged the efficacy of the MMR vaccine. However, clinical symptoms, 5 Journal of Immunology Research complications, viral shedding, and transmission associated with mumps infection have been shown to be reduced in vaccinated individuals, demonstrating a benefit of this vaccine [16]. There was no significant difference among the cases without MuCV in the 2006-2010 birth cohorts (χ 2 = 8:22, p = 0:084); it showed that the sampling was balanced between birth years.…”

Evaluation of Immunity for Mumps among Vaccinated Medical Students

“…Recent findings in the literature highlighted that mumps outbreaks can occur in heavily vaccinated populations, such as HCWs, and mainly in young adults. Many factors have been considered to explain mumps outbreaks in those highly vaccinated populations: heterogeneous vaccine uptake and primary and secondary vaccine failure (immune escape and waning vaccine-induced immunity) [31].…”

“…Waning vaccine-induced immunity accounts for the fall in vaccine immunity over time, determining an inadequate immune response, that leads to virus spread, making adults at higher risk to be infected than children. Potential waning immunity has been reported in recent mumps outbreaks that occurred in Europe that involved young adults who received two doses in childhood [30][31][32][33].…”

Genetic Analysis Reveals Differences in CD8+ T Cell Epitope Regions That May Impact Cross-Reactivity of Vaccine-Induced T Cells against Wild-Type Mumps Viruses

“…However, in the last decade, again several mumps outbreaks have been reported, especially among vaccinated young adults. Waning of vaccine-induced immunity is considered to play a central role in the re-emergence of mumps among vaccinated young adults [ 1 , 2 , 3 , 4 , 5 ]. However, antigenic differences between the currently circulating wild-type viruses and the vaccine virus may further lead to reduced vaccine-induced immunity.…”