Fig. 3

Position of the 50% separatrix line as the R ₀ profile of OPV2 varies, at constant λ = 60 days, N _IPV = 1, c = 1. Each separatrix line, for a given scenario, divides the region of parameter space in which OPV2 survival is estimated to be < 50% probable from the region in which OPV2 survival is estimated to be > 50% probable. The “less probable” region is always the region left and below the separatrix line (that is, less connectivity or less time since cessation reduces the probability of survival), and the “more probable” region for a given scenario is above and to the right of the corresponding separatrix line. The solid and dashed lines, respectively, indicate g = 0.5 and g = 0.25, while the cyan, red, gray, and black lines, respectively, indicate R _0f values of 3, 2, 1.5, and 1.2. The thin black dashed box indicates migration rates that are preferred by a calibration to a single traveling WPV1 outbreak in the region, in 2008. The final R ₀ is observed to have the dominant effect, with the risk at a given time point and migration rate decreasing with R _0f as expected. The initial R ₀ multiplier has a comparatively small effect, but a lower initial R ₀ does also mitigate the survival risk