Fig. 8

Effect of different drug efficacy and sensitiveites for the second-line regimen on HIV disease progression. a and b denote the CD4 T cell counts and viral loads, respectively. Black curve represents the first-line treatment only, purple and pink curves show the cases of switching from first-line regimen to the second-line regimen without and with improving drug efficacy, respectively. Parameter values for first-line regimen: \(\tau _{50}=50, \bar {\tau }_{50}=150, \eta =0.95\), \(\bar {\eta }=0.6, l=0.935\); Parameter values for the second-line regimen: \(\tau _{50}=30, \bar {\tau }_{50}=100\), \(\eta =0.95, \bar {\eta }=0.8\), l=0.92