Fig. 4.

Comparison of results from model (3) with the four mortality schedules described in Fig. 3. Plots (a)–(d) show both the corresponding contour surfaces of the minimized value for ${\mathcal{R}}_{v\text{min}}$ and optimal vaccination rates (${\widehat{\chi }}_1$, ${\widehat{\chi }}_2$, ${\widehat{\chi }}_3$).