Fig. 1.

Overview of model. C, carriage; I, invasive pneumococcal disease; NV, no vaccine; V¹, received one primary dose; V², received two primary doses (only applicable to the 2 + 1 schedule); V³, received the booster dose. Compartments relevant to vaccine doses (both carriage and susceptible) are further stratified into ‘no immunity’ and ‘partial immunity’ induced by vaccine effectiveness, age group and serotype group. Orange arrows indicate 2 + 1 schedule dynamics and blue arrows indicate 1 + 1 schedule dynamics. Grey arrows are applicable to the dynamics of both vaccine schedules.