Assessing the cross-reactivity of mumps antibody between the vaccine genotype A and the circulating genotype G

Recent mumps outbreaks have been observed in vaccinated young adults due to MuV genotype G, whereas the current vaccine is a mixture of two genotype A strains. These outbreaks could be attributed to waning vaccine immunity or antigenic differences between the vaccine and circulating MuV, HN, and F glycoproteins. These glycoproteins are essential targets for the immune system, and antigenic variations may reduce the recognition of mumps antibodies, rendering the population susceptible to MuV. We established stable cell lines expressing the MuV glycoproteins to study cross-reactivity between genotype A and genotype G. Cross-reactivity of antibodies between genotypes was assessed by IFA analysis using patient sera from vaccinated individuals without genotype G infection (vaccinated-only), unvaccinated individuals with a history of genotype G infection (infected-only), and vaccinated individuals with genotype G infection (vaccinated-infected). A limiting dilution assay was used to determine antibody titer, defined as the reciprocal of the last serum dilution at which fluorescence could be detected, and the geometric mean titer (GMT) was calculated. Titer ratios were calculated by dividing the genotype A titer by the genotype G titer, and the arithmetic mean was then calculated. Titer ratios showed that the vaccinated-only individuals had a higher titer for genotype A than for genotype G. In contrast, the infected-only individuals had a lower titer for genotype A compared to genotype G. Notably, no difference in titer ratio was observed for individuals vaccinated and infected with mumps. Additionally, a comparison of GMT in different groups showed that vaccinated-only individuals had lower titers for genotype G than infected-only and vaccinated-infected individuals. These results show a differential antibody response to vaccine vs. wild-type strains of MuV, which may explain the increased susceptibility of mumps in vaccinated young adults. However, there is no correlatio