Figure 3: Effect of varying key parameters. Parameters and initial conditions have the values in Table 1. There is no loss of individual immunity ( 𝑘 r e c = 0 ; (10), Figure 1) and no seasonal forcing ((18); 𝑠 e n v = 0 ). In each case, the value of the altered parameter, basic reproductive ratio 𝑅 0 (20), and total hospital admissions (HA, the integral of 𝐼 h o s 2 , (5)) are given; the curve for the default parameters is thickened and indicated. (a) Changes to infection parameter β. (b) Changes to 𝑘 i n f ( = 𝑘 s i c = 𝑘 h o s = 𝑘 a s y ; Figure 1). (c) Changes to the initial (time t = 0) immune fraction in the recovered category, 𝑓 r e c 0 . This is achieved by altering the time t = 0 value of 𝑛 r e c state variable (Figure 1) to 𝑛 r e c ( 𝑡 = 0 ) = 𝑓 r e c 0 𝑛 c i t y (Table 1, (22)).