RotavirusThe VMI has developed a model assessing the relationship between spatio-temporal variability in the timing of rotavirus epidemics in the United States and variation in birth rates. Historically, annual rotavirus activity in the United States has started in the southwest in late fall and ended in the northeast 3 months later; this trend has diminished in recent years. Traveling waves of infection or local environmental drivers cannot account for these patterns.
A transmission model calibrated against epidemiological data shows that spatiotemporal variation in birth rate can explain the timing of rotavirus epidemics. The recent large-scale introduction of rotavirus vaccination provides a natural experiment to further test the impact of susceptible recruitment on disease dynamics. The model predicted a pattern of reduced and lagged epidemics post vaccination, closely matching the observed dynamics. Armed with this validated model, we explored the relative importance of direct and indirect protection, a key issue in determining the worldwide benefits of vaccination.
The VMI plans to extend the U.S.-based analysis to the context of developing countries, where rotavirus remains a substantial cause of childhood morbidity and mortality and disease dynamics differ. The high birth rates of developing countries may help explain why rotavirus exhibits less seasonal variation in such settings, although climatic factors could also play a role. In addition, rotavirus vaccine efficacy remains somewhat unclear in developing country settings and could be lower than in the United States because of several factors that might interfere with vaccine performance (e.g., presence of maternal antibodies, high levels of coinfection with other enteropathogens, higher rates of malnutrition, and greater prevalence of uncommon rotavirus strains). Differences in population demographics, epidemiology of rotavirus disease, and vaccine effectiveness would need to be carefully considered when assessing the benefits of vaccination in developing countries, and the vaccine experience of industrialized nations may not directly translate to countries with high rotavirus mortality burden. Models on rotavirus dynamic patterns will provide additional tools for public health decision making on vaccine introduction, given the disease situation and cold chain capacity in specific countries.