OBJECTIVES: 70% of new HIV infections in the United States (U.S.) occur among men who have sex with men (MSM). Ongoing prophylactic HIV vaccine efficacy trials for MSM may provide efficacy evidence, but the long-term impact of future HIV vaccines is not clear. This study aims to evaluate the long-term health outcomes of a potential HIV vaccine in the U.S. MSM population under different scenarios of efficacy, durability, and coverage.

METHODS: We developed an agent-based model simulating the sexual transmission of HIV in an active U.S. MSM population (13-65yo), where they were offered a hypothetical HIV vaccine along with condom use and pre-exposure prophylaxis (PrEP). We validated the model by comparing model-estimated HIV prevalence and incidence to the published estimates. We simulated long-term outcomes over 50 years (2025-2075) for no HIV vaccine and under multiple HIV vaccine scenarios with different efficacy, coverage, durability, and booster frequency combinations. For each scenario, we estimated reductions in HIV incidence, prevalence, and mortality.

RESULTS: Under the status quo (i.e., no vaccination), over 1.3 million new HIV infections were estimated to occur between 2025-2075. Comparatively, a HIV vaccine with 30% efficacy and 30% uptake could avert 73,743 new infections (5.43% reduction) by 2075; a vaccine with 90% efficacy, 60% uptake, 2 years durability, and booster at 3 years would avert 495,480 infections (36.46% reduction). The percentage reduction in new HIV infections was dependent on vaccine durability and booster frequency, ranging between 6.63% (No durability and Booster at 5 years) to 20.08% (2 years durability and Booster at 3 years), at 70% efficacy and 45% coverage.

CONCLUSIONS: Reductions in HIV incidence can be achieved with lower efficacy and higher coverage vs. higher efficacy and lower coverage. Therefore, even a partially efficacious HIV vaccine with modest efficacy could substantially reduce HIV incidence, especially when the uptake is high.