Key strategies to reduce HIV incidence in the US are 1) improving diagnosis, care and treatment of people living with HIV (PLWH), and 2) delivering pre-exposure prophylaxis (PrEP) to people at risk for HIV. National HIV/AIDS Strategy (NHAS) 2020 goals provide targets for the first strategy, including increasing to 90% the proportion of PLWH who are diagnosed, to 85% the proportion linked to care (LTC), and to 80% the proportion diagnosed who achieve VLS. Clinical trials have established a large reduction in HIV transmission risk among PLWH who achieve VLS and the efficacy of PrEP in preventing HIV among men who have sex with men (MSM), people who inject drugs (PWID), and high-risk heterosexuals (HRH). However, the effectiveness of PrEP when layered onto improvements in the diagnosis, care and treatment of PLWH has not been well established.
We developed a dynamic, compartmental model of HIV transmission. In the base case, we estimated that in 2015, 87% of PLWH were diagnosed, 80% LTC and 36% VLS among diagnosed. In one scenario, we increased diagnosis to 90%, LTC to 85% and VLS to 60% by 2020. We repeated that scenario with VLS increased to 80%. For the base case and scenarios, we assessed the effect on HIV incidence from 2015 to 2020 of improvements in diagnosis, LTC and VLS alone. We then assessed the marginal benefit of initiating PrEP in 2015 among 40% of high-risk MSM, 10% of PWID and 10% of HRH and maintaining constant coverage through 2020. We applied a 96% reduction in HIV sexual transmission to PLWH who achieved VLS and assumed PrEP efficacy of 73% for MSM, 75% for HRH and 49% for PWID.
In the base case, PrEP reduced HIV incidence by 18% (48,221 cases) over 5 years. Compared with the base case, improving to 90% diagnosed, 85% LTC and 60% VLS among diagnosed reduced incidence by 34% (88,908 fewer cases); the marginal benefit of adding PrEP was an additional 12% (31,988 cases) reduction. Compared with the base case, the scenario with 80% VLS reduced incidence by 63% (168,132 cases); the marginal benefit of PrEP was an additional 7% (16,929 cases).
Increasing diagnosis, care and treatment of PLWH resulted in large decreases in HIV incidence by 2020. The marginal benefit of PrEP decreased as diagnosis, care and treatment improved. However, even at high levels of viral load suppression, PrEP continued to achieve reductions in HIV incidence over 5 years.