Fig 1. Schematic representation of the HIV model.

The boxes represent the model compartments. The arrows represent the flows (or transitions) between compartments. The model splits the population into five groups: susceptible individuals (S), HIV-positive individuals (not on ART) with ≤ 350 CD4 cells/mm³ (I₁), HIV-positive individuals (not on ART) with > 350 CD4 cells/mm³ (I₂), HIV-positive individuals on ART (T), deceased individuals (D). λ _S denotes the force of infection, λ _I the immunosuppression rate, λ _T the treatment rate, and μ the compartment-specific mortality rate. All the compartments are sex- and age-specific.