  The 2014-2015 Ebola Virus Disease (EVD) epidemic in West Africa was the
largest ever recorded, representing a fundamental shift in Ebola epidemiology
with unprecedented spatiotemporal complexity. We developed spatial transmission
models using a gravity-model framework to explain spatiotemporal dynamics of
EVD in West Africa at both the national and district-level scales, and to
compare effectiveness of local interventions (e.g. local quarantine) and
long-range interventions (e.g. border-closures). Incorporating spatial
interactions, the gravity model successfully captures the multiple waves of
epidemic growth observed in Guinea. Model simulations indicate that
local-transmission reductions were most effective in Liberia, while long-range
transmission was dominant in Sierra Leone. The model indicates the presence of
spatial herd protection, wherein intervention in one region has a protective
effect on surrounding regions. The district-level intervention analysis
indicates the presence of intervention-amplifying regions, which provide
above-expected levels of reduction in cases and deaths beyond their borders.
The gravity-modeling approach accurately captured the spatial spread patterns
of EVD at both country and district levels, and helps to identify the most
effective locales for intervention. This model structure and intervention
analysis provides information that can be used by public health policymakers to
assist planning and response efforts for future epidemics.
