Modeling the Potential Impact of Scaling Up Event-Driven PrEP Among Gay, Bisexual, and Other Men who have Sex with Men

BACKGROUND: Event-driven preexposure prophylaxis/PrEP (EDP), or PrEP taken around the time of sex, could be a preferred option over daily PrEP among cisgender gay, bisexual, and other men who have sex with men (MSM). However, recommendations for EDP versus daily dosing require consideration of optimal strategies for HIV prevention based on heterogeneous behavioral and biological PrEP indications. METHODS: We used network-based mathematical HIV transmission modeling to understand the potential population-level impact of implementing EDP alongside daily PrEP using the 2-1-1 dosing schedule: 2 pills on the day of sex, 1 pill a day after, and 1 pill 2 days after. We simulated HIV transmission among 100,000 MSM in Atlanta, Georgia over 10 years. Compared to a baseline scenario with only daily PrEP and no EDP, we tested counterfactual scenarios that increased EDP use by changing initiation rates, expanding EDP to MSM not indicated for daily PrEP, and targeting EDP among MSM with low daily PrEP adherence who discontinued daily PrEP. RESULTS: Increasing EDP initiation such that overall PrEP use was nearly double that at baseline (28.5% vs. 16.1%) yielded a percent of infections averted (PIA) of 18.3%. Expanding eligibility for EDP to any sexually active MSM resulted in a PIA of 15.8%. Targeting EDP for MSM discontinuing PrEP did not yield population-level improvements. Increasing initiation of EDP had a greater impact on PIA compared to improving EDP adherence. CONCLUSIONS: Using EDP to improve overall PrEP use resulted in reductions in HIV incidence, while targeted EDP initiation for MSM with low daily PrEP adherence did not improve outcomes over 10 years.