Fig 6. Effect of evolution on the suppression of immunity by impairment parameters.

The final level of immunity to the vaccine antigen (X) depends heavily on the inhibitory parameters k_X and k_Y—which respectively describe how strongly immunity to the vaccine (X) and revertant (Y) suppress the viral populations. The left plot considers the absence of revertant, hence no evolution. The right panel introduces revertant at 3/4 the inoculum, with the same total inoculum size as in the left panel. The revertant reduces immunity X, but the effect of increasing k_X is not made worse by the revertant. Intrinsic fitness differences are absent; mutation rate of vaccine to revertant is set to 0 and fitness benefit of revertant (c) is 0. Equations, initial conditions and parameter values not shown here are given in S1 Appendix; R code is included in S1 File.