Figure 9.

The bifurcation diagram (a) in a strong immune response, that is, p = 0.01, for two values of γ (in years^-1): 0.0001 (backward bifurcation, labelled 1) and 0.00016 (forward bifurcation, with β₀ = 204.626 $year{s}^{-1}$, labelled 2). We give, in (b) and (c) respectively, a zoom near the lower bound (${\beta }_c^1=\text{208}\text{.82 }year{s}^{-1}$) and threshold (β₀ = 326.19 years^-1) transmission coefficients with respect to the backward bifurcation.