Disentangling the causes of mumps reemergence in theUnited States br

Over the past two decades, multiple countries with high vaccine coverage haveexperienced resurgent outbreaks of mumps. Worryingly, in these countries, a highproportion of cases have been among those who have completed the recommendedvaccination schedule, raising alarm about the effectiveness of existing vaccines. Twoputative mechanisms of vaccine failure have been proposed as driving observed trends:1) gradual waning of vaccine-derived immunity (necessitating additional booster doses)and 2) the introduction of novel viral genotypes capable of evading vaccinal immunity.Focusing on the United States, we conduct statistical likelihood-based hypothesistesting using a mechanistic transmission model on age-structured epidemiological,demographic, and vaccine uptake time series data. We find that the data are mostconsistent with the waning hypothesis and estimate that 32.8% (32%, 33.5%) ofindividuals lose vaccine-derived immunity by age 18 y. Furthermore, we show usingour transmission model how waning vaccine immunity reproduces qualitative andquantitatively consistent features of epidemiological data, namely 1) the shift in mumpsincidence toward older individuals, 2) the recent recurrence of mumps outbreaks, and3) the high proportion of mumps cases among previously vaccinated individuals.