Figure 1

A semi-Markov model. The provision of HIV vaccination was on a voluntary basis, so the target population had the option of accepting or refusing the vaccine. The model consists of five health states: (1) HIV negative; (2) HIV positive without symptoms (asymptomatic); (3) progression into HIV with related symptoms (symptomatic); (4) AIDS state during antiretroviral treatment (ART), which includes three sub states, i.e., the first-line ART, the second-line ART, and the third-line ART regimens; and (5) death due to HIV infection and other causes. The arrows represent the probability of transitions from one state to another.