Despite the inhibitory effects of IFN, W remained fitter than D. Because c = 0, this was strictly due to spatial structure which, in turn, emerged from the diffusion-reaction infection and immunity processes and allowed W to be on average less adversely affected by IFN-mediated immunity than D. These results suggest that spatial structure is a key determinant of the evolution of IFN suppression in viruses. Here, IFNA1 is linked to infection.