FIG 3.

(A) Compensatory immunity alters the fitness of escape variant infection in the Hh and hh individuals. We show the viral fitness in the hosts of different genotypes and infection histories (being previously infected by the WT only or both WT and MT). The fitness of WT infection is 1 in all hosts (shown as the blue dot on the fitness scale). The fitness of MT in HH, Hh, and hh hosts are (1 – m), (1 – m + rs), and (1 – m + s), respectively (shown as the red arrows in the top panel and black dots on the fitness scale). Subsequent MT infections of Hh and hh hosts result in lower viral fitness, [1 – m + rs(1 – c)] and [1 – m + s(1 – c)], which is dependent on the extent of compensatory immunity and reduces the selective advantage by c and the dominance coefficient, r (shown as the red dashed arrows in the bottom panel). (B) Diagram illustrating the epidemiology of infections with WT (W, shown in blue) and MT (M, shown in red) in any of the three genotypes. Susceptible and immune hosts are indicated by S and R, respectively. The host genotype is indicated by the superscript j (j = 1, 2, and 3 for HH, Hh, and hh), and the prior infection status is indicated by a subscript (W for WT and WM for WT and MT).