Fig. 2

Attack rates are increased in models with variable duration of immunity. A comparison of the attack rates with a constant (blue) and a variable (red) duration of immunity without vaccination (a) and with vaccination (with a coverage of 20%) (b). With vaccination the attack rates are significantly higher in the scenario with variable duration of immunity, while in both cases the average duration of immunity is identical. Shown are median values of 1,000 simulations. Black error bars denote the 2.5−97.5 percentiles. For each scenario, the mean infection attack rate is calculated over a period of 100 years after a burn-in period of 50 years