The spatial homogeneity coefficient depends only on the connection strength expressed in commuters vcw and the average reproductive number R 0~a3 of the fully adapted strain. Though it only considers the fully adapted strain, we expect this coefficient to be a good approximation for a multi-strain model as the vast majority of infectious hosts will transmit the fully adapted strain in the case of an emergence. Figure 6 gives an overview of the influence of spatial heterogeneity as a function of vcw. Effectively, spatial heterogeneity is negligible once a critical number of ten commuters connect the two communities. This is a very low threshold, and empirical data shows that the probability of having a community with less than the critical number of ten commuters is approximately 1% for all our data combined.