Figure 4: Dynamics with loss of individual immunity. Individuals now lose immunity ( 𝑘 r e c = 1 ; Figure 1). Parameters and initial conditions have the values in Table 1. (a) Short-term dynamics: susceptible 𝑛 s u s and delayed 𝑛 d e l numbers are calculated with (2) and (1), the dynamic reproductive ratio 𝑅 d y n with (22), and hospital admission rate 𝐼 h o s 2 with (5). (b) Longer-term dynamics.