Figure 2: The contact network of the subpopulation. (a) An equivalent contact network to the population structure is shown in Figure 1(c). The long-distance traveller has two high-risk exposures, denoted by node 1 and node 2 and only suffers from occasional risk of infection from other individuals. (b) The distribution of the exposures for individuals in the subpopulations in our model. The dashed red line has a slope −2.19.