Fig 2. Schematic of the transmission model.

Sⁱ(a) denotes the proportion of uninfected persons of age a and sex i (i ∈ {♀, ♂}), and Lⁱ(a) and Bⁱ(a) are the corresponding proportions of infected persons without and with increased antibodies, respectively. The infection and re-infection rates are given by λⁱ(a) and zλⁱ(a), and the reactivation rates are given by ρⁱ(a). We consider model scenarios with and without reactivation/re-infection in the B compartment (i.e. including or excluding the loop to the right of B).