Figure 3: Effect of varying key parameters. Parameters and initial conditions have the values in Table 1. There is no loss of individual immunity (; (10), Figure 1) and no seasonal forcing ((18); ). In each case, the value of the altered parameter, basic reproductive ratio (20), and total hospital admissions (HA, the integral of , (5)) are given; the curve for the default parameters is thickened and indicated. (a) Changes to infection parameter β. (b) Changes to ; Figure 1). (c) Changes to the initial (time t = 0) immune fraction in the recovered category, . This is achieved by altering the time t = 0 value of state variable (Figure 1) to (Table 1, (22)).