Fig. 1.

Structure of the dynamic model of HIV-1 transmission, ART rollout and resistance emergence (upper panel), and model outputs with colours corresponding to Figs. 2 and 3 (lower panel). The population is split into six compartments: susceptible to HIV-1 ($S$); infected with a drug-sensitive strain and either untreated ($I$) or treated with first-line ART ($T$); infected with a drug-resistant strain and either untreated ($J$), treated with first-line ART ($U$) or treated with second-line ART ($V$). The model has ten parameters: transmission rate $\beta$; maximal treatment rate $\tau$ scaled by a sigmoid function $f\left(t,,,\nu ,,,\xi \right)$ (controlled by two parameters for shift $\nu$ and slope $\xi$); rate at which de novo NNRTI resistance emerges during treatment ($\omega$); rate of switching to second-line ART ($\kappa$); rate of AIDS-related mortality ($\delta$); rate of background mortality ($\mu$); rate of population growth ($\eta$); and the initial proportion of NNRTI resistance $\iota$ (not shown)