A DYNAMIC HIV-TRANSMISSION MODEL FOR EVALUATING THE COSTS AND BENEFITS OF VACCINE PROGRAMS

We developed a dynamic model of HIV transmission to evaluate the costs and benefits of HIV-vaccine programs in a population of homosexual me n. We examined how changes in highrisk sexual behavior and the growth pattern of the epidemic influence the cost-effectiveness of preventive vaccines and of therapeutic vaccines. We found that the effect of red uctions in condom use is more important for therapeutic vaccines than for preventive vaccines. Therapeutic vaccines may increase HIV seropre valence in the population, unless the vaccine program is accompanied b y increased condom use. Epidemic growth patterns also influence the co st-effectiveness of both vaccines, but the effects are more pronounced for preventive vaccines, which are more cost-effective in an early-st age epidemic than in a late-stage epidemic.