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Estimating benefits of using on-demand oral prep by MSM: A comparative modeling study of the US and Thailand
Sarah E Stansfield1, Mia Moore1, Marie-Claude Boily2
1Fred Hutchinson Cancer Center, Seattle, WA, United States.
Background:
Daily and on-demand pre-exposure prophylaxis (PrEP) are effective at preventing HIV acquisition among men who have sex with men (MSM), but only daily PrEP is approved in the US. On-demand PrEP may improve uptake and adherence. We identify sub-groups of MSM who would benefit from on-demand PrEP and determine effectiveness achieved if individuals used their optimal regimens.
Methods:
Using data from the HPTN 067 study (study period 2012-2014), we created an individual-based stochastic model of HIV risk in two synthetic MSM populations with parameters separately estimated using data from Harlem, US, and Bangkok, Thailand. Agents were assigned daily and on-demand PrEP for six months each. Two personalized PrEP assignments: optimal, based on improved predicted effectiveness and reduced pill burden, and adherence-based, using daily PrEP adherence, were simulated for another six months.
Findings:
Simulated on-demand PrEP was optimal for approximately one-third of MSM. It was assigned mainly to those with low daily PrEP adherence (88% (Harlem), 95% (Bangkok) of MSM with daily PrEP adherence <40%). Mean effectiveness was slightly higher in the full synthetic population with optimal PrEP assignment compared to universal daily PrEP. Among MSM for whom on-demand PrEP was optimal, mean effectiveness improved by 18 (Harlem) and 7 percentage points (Bangkok). Comparable predicted effectiveness was achieved if on-demand PrEP was assigned to the population with daily PrEP adherence <50%. There was no advantage in assigning on-demand PrEP by sex act frequency.
Interpretation:
On-demand PrEP could benefit many MSM by increasing effectiveness or decreasing pill burden with similar effectiveness. On-demand PrEP may be an effective alternative to daily PrEP for individuals with difficulty taking daily PrEP consistently. Results were similar for Harlem and Bangkok, indicating that these conclusions were robust in populations with different overall adherence levels and may inform future public-health policies.
Funding:
US NIH grant UM1 AI068617.
Insights
On-demand pre-exposure prophylaxis (PrEP) can improve HIV prevention effectiveness for many men who have sex with men (MSM), especially those with lower daily adherence. This strategy offers a flexible alternative to daily PrEP, potentially increasing uptake and adherence.
Area of Science:
- HIV Prevention Research
- Pharmacology
- Public Health
Background:
- Daily pre-exposure prophylaxis (PrEP) is effective for HIV prevention in men who have sex with men (MSM), but only daily regimens are US-approved.
- On-demand PrEP may enhance uptake and adherence among MSM.
- Identifying subgroups of MSM who would benefit most from on-demand PrEP is crucial for optimizing effectiveness.
Purpose of the Study:
- To identify specific subgroups of MSM who would benefit from on-demand PrEP.
- To determine the potential effectiveness of on-demand PrEP when individuals use their optimal regimens.
- To compare the effectiveness of personalized PrEP assignments (optimal vs. adherence-based) with universal daily PrEP.
Main Methods:
- Utilized data from the HPTN 067 study (2012-2014) to create individual-based stochastic models of HIV risk in synthetic MSM populations (Harlem, US, and Bangkok, Thailand).
- Simulated six-month periods of daily and on-demand PrEP for all agents.
- Introduced personalized PrEP assignments (optimal and adherence-based) for an additional six months to assess effectiveness and pill burden.
Main Results:
- On-demand PrEP was found to be optimal for approximately one-third of MSM, particularly those with low daily adherence (<40%).
- Mean effectiveness was slightly higher with optimal PrEP assignment compared to universal daily PrEP across synthetic populations.
- Significant effectiveness improvements were observed for MSM for whom on-demand PrEP was optimal (18 percentage points in Harlem, 7 in Bangkok).
Conclusions:
- On-demand PrEP offers a viable strategy to increase HIV prevention effectiveness or reduce pill burden for many MSM.
- It can serve as an effective alternative for individuals struggling with consistent daily PrEP adherence.
- The robustness of findings across different adherence levels suggests broad applicability for informing public health policies.
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