Background: The ANRS IPERGAY trial demonstrated among MSM a 86% relative reduction of HIV-1 incidence with on demand PrEP in the TDF/FTC arm (2 infections, 219 person-years (py) of follow-up (FU), incidence: 0.91/100 py) as compared to the placebo arm (14 infections, 212 py of FU, incidence: 6.60/100 py). Participants in this trial used a median of 15 pills /month and had a median of 10 sexual intercourse /month. We wished to investigate whether on demand PrEP remained effective among participants having less frequent sexual intercourse and using fewer pills.
Methods: Assuming that participants with less frequent sexual intercourse would use fewer pills, and because individual patterns of pill use showed large intra-participant variability over time, we focused our analysis on person-time between 2 consecutive visits when participants used < 15 pills /month and PrEP was used “systematically or often” during sexual intercourse, and not “from time to time or never”. We then cumulated in each arm FU time spent with this pattern of pill use. A 4th generation HIV-1/2 ELISA assay was performed at each visit allowing to date the time of HIV-infection. Incidence rates of HIV-infection/100 py in both arms were then compared using mid-p exact test.
Results: Six HIV-1 infections occurred during FU among participants using < 15 pills/month taken “systematically or often” during sexual intercourse: 6 in the placebo arm (incidence: 9.3/100 py, total FU time: 64.8 py) and 0 in the TDF/FTC arm (incidence: 0/100 py, total FU time: 68.9 py, p=0.013). The relative reduction of HIV incidence was 100% (95% CI: 20-100). During these follow-up periods, a median of 5 (IQR: 2-10) sexual intercourse/month were reported and a median of 9.5 (IQR: 6-13) pills/month were used. Restricting the analysis to periods when participants reported at least one condomless sexual act yielded similar results with HIV incidence of 12.3/100 py in the placebo arm (6 infections, 48.8 py of FU) and 0/100 py in the TDF/FTC arm (0 infection, 54.3 py of FU, p=0.011).
Conclusions: On-demand PrEP with TDF/FTC remains highly effective in MSM having infrequent sexual intercourse.