Dapivirine ring HIV-1 prevention effectiveness for women engaged in vaginal and anal intercourse: insights from mathematical modeling

The dapivirine vaginal ring reduces risk of HIV-1 acquisition in acts of vaginal intercourse (VI), and though it does not offer HIV-1 protection in acts of anal intercourse (AI), it may provide some overall risk reduction for women for whom the majority of sex acts are vaginal. We estimated the protective effect of the ring among women with high ring adherence engaged in both vaginal and anal intercourse.We developed a microsimulation model using data from the MTN-020/ASPIRE trial. Among women who reported any AI, we estimated the proportion of all sex acts that were AI. Model scenarios varied this proportion among women engaged in both VI and AI from 5-30%, including the trial-observed median proportion of 6.3% of all acts being AI. In primary analyses, dapivirine ring efficacy was model-calibrated at 70% for vaginal exposures and assumed to be 0% for anal exposures.Among highly-adherent women for whom 6.3% of sex acts were AI, the ring reduced HIV-1 risk by 53% (IQR: 44, 60), with a decline to 26% (IQR: 16, 36) among women for whom 30% of acts were AI. Ring effectiveness was less than 40% among women for whom AI accounted for greater than 16% of all sex acts, although this represented less than 5% of all women in the ASPIRE trial.For the vast majority of women, including those who engage in AI, because most HIV-1 risk occurs in acts of vaginal sex, the dapivirine vaginal ring can provide important HIV-1 protection.