The epidemic dynamics of measles are the best understood among acute infections. Powerful herd immunity leads to a tendency for multi-annual outbreaks; these are forced mainly by seasonal variations in infection rates leading to high amplitude cycles and potentially chaotic dynamics. Though largely eradicated from the developed world through vaccination, measles remains a significant public health issue in the developing world. Our analyses of measles dynamics in the Sahelian nation of Niger show that the combination of strong seasonal forcing due to the annual rain cycle and exceedingly high birth rates leads to locally erratic, high amplitude outbreak dynamics with a high degree of epidemic fade-out. At the national scale, however, measles appears to persist in regular annual outbreaks. A weakly coupled metapopulation can lead to persistent dynamics through rescue effects while maintaining local asynchrony. In Niger, however, strong seasonality due to the annual rainy season forces synchrony in the timing of epidemic troughs, increasing the likelihood of metapopulation extinction. Increased coupling between patches tends to promote metapopulation persistence under strong seasonality but results in locally annual dynamics and phase locking. Through analysis of long-term spatio-temporal data on measles incidence in Niger, we explore how heterogeneities in coupling can lead to both long-term persistence and maintenance of locally erratic dynamics.
