Migration and The Equilibrium Prevalence of Infectious Diseases

This paper models how migration both influences and responds to differences in disease prevalence between cities, regions and countries, and show how the possibility of migration away from high-prevalence areas affects long-run steady state disease prevalence. We develop a dynamic framework where both migration and prevention behaviour respond to the prevalence of disease, to the costs of migration and of treatment, and to current and anticipated health regulations. The model treats disease prevalence as an endogenous consequence of other features of the areas concerned, notably their economic endowments. It explores how pressure for migration in response to differing equilibrium levels of disease prevalence causes countervailing differences in city characteristics, notably in land rents. Competition for scarce housing in low-prevalence areas can create pressures for segregation, with disease concentrated in high-prevalence "sinks". We show that multiple steady states may exist and explore their comparative static properties. In particular we find that migration can have positive health benefits, in that reductions in barriers to migration can reduce steady-state disease incidence in low-prevalence areas while having no impact on prevalence in high-prevalence areas. This may have important consequences for policy; in some circumstances, public health measures may need to avoid discouraging migration away from high-disease areas.