Cumulative frequency of infection and age-specific incidence at different forces of infection. A. Cumulative frequencies of HEV infection and B. age-specific incidence elicited by different forces of infection are compared. Assumed values for the forces of infection were 0.01 (thick black), 0.03 (thin black) and 0.05 (thick gray) days-1. See eqs. 6 and 7 for details of the model.