Simulations to Evaluate HIV Vaccine Trial Designs

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Abstract
Many HIV vaccine trials have been proposed to evaluate susceptibility of individuals. However, vac cines may also affect an epidemic's course at the population level by altering the infectiousness of vaccinated individuals who become infected. A vac cine trial design that does not estimate both suscep tibility and infectiousness might reject a proposed vaccine that is capable of halting the HIV epidemic. We describe a vaccine trial design called the Retro spective Partner Trial (RPT), which can quantify vaccine effects on both susceptibility and infectious ness. We describe HIVSIM, a simulation environ ment that generates simulated populations and al lows for empirical evaluation of the statistical power of the RPT. HIVSIM explicitly models a number of factors which influence transmission and preva lence, and which have proven difficult to model us ing standard models. These factors include the infec tion stage of infected individuals, partnership selec tion, the duration of partnerships and concurrence, and transmission of HIV. The simulation analysis indicates that the RPT design has substantially greater statistical power for identifying vaccines which, in spite of exhibiting poor protection against infection, are nonetheless capable of halting the HIV epidemic by substantially reducing the infectious ness of vaccinated individuals who become infected.