Fig. 8.

(a) Solution trajectories of system (2) illustrating the existence of locally asymptotically stable HIV endemic equilibrium ${\chi }_H^1$ with ${\mathcal{R}}_E^H=0.6394<1$, ${\nu }_1=0.00129>{\overline{\nu }}_1$ and (b) visualization of backward bifurcation in $S_U^H-H_1-T_H$ space. Other parameters are at the same values as in Table 1