Fig. 4

Time after the third vaccine dose (years), versus vaccine efficacy, for a four-dose schedule. Three scenarios are shown. a Fourth dose at 18 months, corresponding to the phase 3 trial data; b intermediate scenario; c fourth dose at 8 months with a higher antibody titre (corresponding to higher efficacy), approximating observed efficacy in the Regules et al. study, and referred to as the ‘modified’ vaccine scenario [6]. The parameters are given in Table 1 and the corresponding antibody titre curves in Additional file 1: Figure S6. In each subplot, the solid line is the median of 2000 simulations, and the dark and light shaded regions represent the 50% and 95% predictive intervals, respectively. Other parameters are those described in White et al, Table 3, for the 5–17-month age category [13]