Demographic transition and the dynamics of measles

Background/Question/Methods

Urban centers, greater than the so-called “critical community size”, are classically thought of as reservoirs for infectious disease, which would be likely to have a stabilizing effect on regional dynamics. However, the demographic transition associated with economic development can change the dynamics of infectious disease both within urban centers and regionally. In developing economies, human populations shift in age-structure towards a greater proportion of adults and tend to become increasingly dense and increasingly mobile. These shifts are often accompanied by increasing variance in wealth distribution and access to health care.  This demographic transition has profound effects for the distribution and persistence of infectious diseases and the application of optimal strategies for control through prophylactic vaccination. We evaluate the dynamics of measles transmission and persistence in response to demographic transition through case studies of transition from rural to urban economies in the Americas, sub-Saharan Africa, and East Asia.

Results/Conclusions

We find that the demographic transition associated with economic development impacts both the persistence of measles transmission in urban centers and, as a consequence, the role of urban centers in epidemiology of measles at the regional scale. We find that rural-urban migration in developing economies can generate greater seasonal fluctuations in population density and measles transmission, which can destabilize persistence in urban areas.  Similarly, urban areas have, on average, higher rates of vaccine coverage, which should reduce the recruitment of susceptible individuals and increase the probability of stochastic local fadeout. We further find that urban centers tend to correlate with an increasing proportion of adult measles cases, which facilitate greater connectivity between communities. The combination of these factors, both increased local instability and higher rates of connectivity, results in a transition in regional dynamics from that of stable persistence in large population centers to one of regional persistence through metapopulation dynamics. We discuss this shift in regional dynamics as a consequence of demographic transmission and the implications for changes in control through vaccination.