Figure 6

The threshold ( β ₀ ) and lower bound ( ${\beta }_c^q$, for q = 0 and 1) transmission coefficients as a function of the incubation rate γ, using values given in Table 1. β ₀ (multiplied by a factor 100) and ${\beta }_c^1$ are decreasing functions, while ${\beta }_c^0$ is an increasing function, with ${\beta }_0>{\beta }_c^0>{\beta }_c^1$. When q = 1, they assume the same value (${\beta }_0={\beta }_c^1=\text{4}\text{.55 }year{s}^{-1}$) at γ = 0.0128 years^-1, and for q = 0, they assume the same value (${\beta }_0={\beta }_c^0=\text{5}\text{.891 }year{s}^{-1}$) at γ = 0.00838 years^-1 (a). At a given γ, the difference between β ₀ and ${\beta }_c^1$ (or ${\beta }_c^0$, which is practically the same) corresponds to the range of β at which two positive solutions are found (b).