Abstract
BACKGROUND: Pre-exposure prophylaxis (PrEP) is an effective and safe intervention approved for use to prevent HIV transmission. PrEP scale-up strategies and clinical practice are currently being informed by modeling studies, which have estimated the impact of PrEP in adult and adolescent MSM populations separately. This partitioning may miss important effects or yield biased estimates by excluding dependencies between populations. METHODS: We combined two published models of HIV transmission among adults and adolescent MSM. We simulated an HIV epidemic among MSM aged 13-39 without PrEP, with PrEP for adult MSM ages (19-39) and with the addition of PrEP for adolescents ages (16-18), comparing percent of incident infections averted (impact), the number of person-years on PrEP per infection averted (efficiency), and changes in prevalence. RESULTS: PrEP use among eligible 19-39 year old MSM averted 29.0% of infections and reduced HIV prevalence from 23.2% to 17.0% over ten years in the population as a whole. Despite being ineligible for PrEP in this scenario, prevalence among sexually active 18 year-olds declined from 6.0% to 4.3% due to reduced transmissions across age cohorts. The addition of PrEP for adolescents ages 16-18 had a small impact on the overall epidemic, further reducing overall prevalence from 17.0% to 16.8%; however prevalence among the sexually active 18 year-olds further declined from 4.3% to 3.8%. CONCLUSIONS: PrEP use among adults may significantly reduce HIV prevalence among MSM and may also have significant downstream effects on HIV incidence among adolescents; PrEP targeting adolescents remains an important intervention for HIV prevention.