Simulation of infection histories. Stochastic simulation of five individual infection histories showing (A) the acquisition of immunity in terms of exposed upsA associated epitopes and (B) the drop in the risk of severe disease with the number of infections; the black lines are the averages of 100 simulations. Left panel: (N, n) = (120, 6), right panel: (N, n) = (200, 10). The insets show how the gap in the immune repertoire, h
, decreases with consecutive infections.