Figure 1.

Schematic diagram of the model. The wild-type population (W) increases at rate r, mutates to the mutant strain at rate $\mu$ and is cleared by antibodies at rate p. The mutant population increases at rate $r(1-c)$, where c is the fitness cost of the mutation; increases by mutation from the wild-type strain at rate $\mu$; and is cleared by antibodies at rate $(1-q)p$, where $(1-q)$ represents reduction in antibody blocking against the mutant. The antibody population increases at the time of each plasma infusion (by fixed amount $A_{inf}$) and decays exponentially at rate d.