Assessing Per-Sex-Act HIV-1 Risk Reduction Among Women Using the Dapivirine Vaginal Ring Randy M. Stalter,1 Tracy Q. Dong,2 Craig W. Hendrix,3 Thesla Palanee-Phillips,1,4 Ariane van der Straten,5,6 Sharon L. Hillier,7,8 Flavia M. Kiweewa,9 Nyaradzo M. Mgodi,10 Mark A. Marzinke,3 Linda-Gail Bekker,11 Lydia Soto-Torres,12 Jared M. Baeten,1,13 and Elizabeth R. Brown2,14; for the MTN-020/ ASPIRE Study Team 1Department of Epidemiology, University of Washington, Seattle, WA, USA; 2Vaccine and Infectious Disease Division, Fred Hutchinson Cancer Research Center, Seattle, WA, USA; 3Department of Medicine, Johns Hopkins University, Baltimore, MD, USA; 4Wits Reproductive Health and HIV Research Institute, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa; 5Center for AIDS Prevention Studies, Department of Medicine, University of California San Francisco, San Francisco, CA, USA; 6ASTRA consulting, Kensington, CA, USA; 7Department of Obstetrics, Gynecology, and Reproductive Sciences, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA; 8Magee-Womens Research Institute, Pittsburgh, PA, USA; 9Research Department, Makerere University-Johns Hopkins University Research Collaboration, Kampala, Uganda; 10Clinical Trials Research Centre, University of Zimbabwe, Harare, Zimbabwe; 11The Desmond Tutu HIV Centre, University of Cape Town, Cape Town, South Africa; 12Division of AIDS, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, USA; 13Departments of Medicine and Global Health, University of Washington, Seattle, WA, USA; and 14Department of Biostatistics, University of Washington, Seattle, WA, USA Background. Confounding introduced by individuals’ sexual risk behavior is potentially a significant source of bias in HIV-1 prevention intervention studies. To more completely account for sexual behaviors when assessing the efficacy of the monthly dapivirine ring, a new longer-acting HIV-1 prevention option for women, we estimated per-sex-act risk reduction associated with product use. Methods. We conducted a secondary analysis of data from MTN-020/ASPIRE, a phase 3, randomized, placebo-controlled efficacy trial of the dapivirine ring that recruited HIV-uninfected, African women aged 18–45 years. With cumulative sex acts as the time scale, we used multivariable Cox regression with inverse probability of censoring weights to estimate HIV-1 risk reduction associated with a rate of dapivirine release indicative of consistent product use. Results. Women in the dapivirine ring group (n = 1187) had an estimated incidence rate of 2.3 (95% confidence interval [CI], 1.8–3.1) HIV-1 acquisition events per 10 000 sex acts versus 3.6 (95% CI, 2.9–4.4) per 10 000 acts in the placebo group (n = 1187). Dapivirine release indicative of consistent ring use was associated with a 63% (95% CI, 33%–80%) per-sex-act HIV-1 risk reduction. Conclusions. These results support the efficacy of the dapivirine vaginal ring for HIV-1 prevention and help to inform decision-making for women, providers, and policymakers regarding product use. Clinical Trials Registration. NCT01617096. Keywords. dapivirine; vaginal ring; preexposure prophylaxis; HIV-1; per sex act. Received 19 February 2023; editorial decision 25 November 2023; published online 14 December 2023 Correspondence: Randy M. Stalter, PhD, MPH, Department of Epidemiology, University of Washington, 325 Ninth Avenue, Box 359927, Seattle, WA 98104 (randystalter@gmail.com). The Journal of Infectious Diseases® 2024;229:1158–65 © The Author(s) 2023. Published by Oxford University Press on behalf of Infectious Diseases Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@ oup.com https://doi.org/10.1093/infdis/jiad550 In sub-Saharan Africa, women and girls account for more than half of new human immunodeficiency virus-1 (HIV-1) infec- tions, underscoring the need for acceptable, novel, safe, and ef- fective biomedical prevention interventions in this region [1]. Oral preexposure prophylaxis (PrEP) with tenofovir disoproxil fumarate and emtricitabine (TDF/FTC) is an important antiretroviral-based prevention strategy and is being scaled up rapidly in areas of sub-Saharan Africa with high HIV-1 bur- den [2]. However, challenges with daily PrEP adherence have been observed in past randomized trials and implementation studies [3–5], indicating that additional options are needed to fit women’s diverse needs and preferences. One such option is the vaginal ring containing the nonnucleoside reverse tran- scriptase inhibitor dapivirine, a product with a demonstrated favorable safety profile and HIV-1 risk reduction efficacy that women can wear continuously and discreetly for up to 1 month [6, 7]. In 2020, the ring received a positive opinion from the European Medicines Agency and prequalification and a recom- mendation from the World Health Organization [8–11]. The ring has since received regulatory approval in multiple coun- tries in eastern and southern Africa [12–14]. As the dapivirine ring becomes an available PrEP option for women, it is important that its efficacy (ie, how well the product works when used under ideal conditions) be thoroughly as- sessed so that women can make well-informed decisions. The dapivirine ring was evaluated in 2 phase 3 efficacy trials in sub-Saharan Africa, MTN-020/ASPIRE and IPM 027/The Ring Study, and was found to be effective, reducing HIV-1 ac- quisition risk by 27% and 31% in intention-to-treat analyses, respectively [6, 7]. As observed in studies of oral PrEP agents [15, 16], efficacy was highly associated with greater adherence, and thus the intention-to-treat findings likely underestimate the product’s efficacy when there are varying levels of adherence in the intention-to-treat population. Further evaluation with objective measures of adherence, however, has helped to further elucidate product efficacy. Within the Partners PrEP Study, a 1158 • JID 2024:229 (15 April) • Stalter et al The Journal of Infectious Diseases M A J O R A R T I C L E D ow nloaded from https://academ ic.oup.com /jid/article/229/4/1158/7473606 by C ynthia W arren user on 07 O ctober 2024 mailto:randystalter@gmail.com https://doi.org/10.1093/infdis/jiad550 case-cohort analysis demonstrated a 91% relative risk reduction (RRR) associated with plasma tenofovir concentrations consis- tent with daily use among TDF/FTC users [17], in contrast to 75% effectiveness of TDF/FTC estimated in the intention-to-treat analysis [15]. Similarly, a substudy of the iPrEx trial found that intracellular tenofovir metabolite concen- trations indicative of 4 or more oral doses per week were predic- tive of 90% HIV-1 risk reduction relative to placebo versus 44% risk reduction in intention-to-treat analysis [18, 19]. For the da- pivirine ring, disproportionately low adherence was seen among certain groups, particularly younger women. A secondary anal- ysis of data from MTN-020/ASPIRE identified reductions in HIV-1 risk of 48% or more among women who demonstrated continuous ring use based on measured rates of dapivirine re- leased from the ring [20]. However, a key factor to consider when further evaluating the efficacy of HIV prevention products in secondary analyses of clinical trial data where exposure groups are no longer random- ized is the potential for confounding by sexual behavior. HIV-1 acquisition is dependent on exposure to the virus through unpro- tected sex, specifically with a partner with HIV-1. However, ana- lytic approaches to evaluating HIV-1 prevention methods that use a standard time scale assume that individuals who are not having sex accumulate risk at the same rate as individuals who are having frequent sex, which can lead to biased efficacy esti- mates if sexual behaviors systematically differ between product use groups. By assessing risk on a sex act scale, periods of time with no sexual activity, and therefore without any chance of ex- posure, would not inform relative risk estimates. This work builds on the previous secondary analysis within MTN-020/ASPIRE by more thoroughly accounting for sexual behavior and estimating per-sex-act risk reduction associated with rates of dapivirine re- lease from returned rings indicative of continuous use. We hy- pothesized that HIV risk reduction estimates will be higher after more thorough accounting of women’s sexual behaviors than previously estimated with dapivirine ring use. METHODS Study Population and Procedures We conducted a secondary, longitudinal analysis of data collected from MTN-020/ASPIRE (NCT01617096), a phase 3 randomized placebo-controlled trial to assess the efficacy of the dapivirine vag- inal ring for prevention of HIV-1 acquisition. Study procedures have been previously described in detail [6]. Briefly, healthy, HIV-uninfected cisgender women between ages 18 and 45 years, sexually active, and using an effective contraceptive method were recruited from 15 sites in Malawi, South Africa, Uganda, and Zimbabwe. Women were randomized 1:1 to use a silicone vaginal ring formulated with 25 mg of dapivirine or an inactive placebo ring and instructed to use the product continuously for 28 days. At monthly visits, women received a resupply of ring as well as serologic HIV-1 testing and product adherence counseling. Safety of ring use was evaluated at each follow-up visit and study product was held for one or more of the following criteria: preg- nancy or breastfeeding, positive HIV-1 rapid test, experience of adverse event or allergic reaction related to the study product, or report of HIV-1 postexposure prophylaxis. Ethics review commit- tees at each site approved the study protocol and all participants provided written informed consent prior to initiation of study procedures. Survey and Laboratory Measures Information on women’s sociodemographic characteristics, family planning use, menses/bleeding, and partner HIV-1 sta- tus and knowledge of ring use were collected by interviewer- administered surveys. HIV-1 testing followed a standardized algorithm. At month- ly study visits, women received 2 separate serological HIV-1 tests. If either test yielded a positive result, confirmatory west- ern blot and HIV-1 RNA testing were performed on sera col- lected at the most recent quarterly visit. Archived sera from previous quarterly visits were also analyzed for HIV-1 RNA if needed to identify the earliest evidence of HIV-1 infection. Testing for STIs and bacterial vaginosis (BV) occurred at the screening visit and then semiannually and when clinically indi- cated. Urine samples were tested for Neisseria gonorrhoeae and Chlamydia trachomatis using a nucleic acid amplification test. Rapid tests for Trichomonas vaginalis were conducted on vag- inal swabs. Vaginal fluid samples were assessed for BV by Gram stain using the Nugent score. Adherence Measures Ring adherence was evaluated using multiple objective mea- sures. First, stored plasma specimens from quarterly study visits were analyzed for dapivirine concentrations via a previously de- scribed ultraperformance liquid chromatography-tandem mass spectrometry assay [21]. Second, approximately 1 year after study enrollment began, used rings were collected at monthly visits and analyzed for quantities of residual dapivirine to assess cumulative use. Residual dapivirine in rings was collected using acetone extraction and then quantified using high-pressure liq- uid chromatography. The amount of drug released during intra- vaginal use was estimated by subtracting the amount of residual dapivirine measured in the ring from the batch-specific dapivir- ine loading mass. Given that women may not have returned to the clinic exactly 4 weeks after their previous visit, we standard- ized the amount of dapivirine released to 28 days of use. In pre- vious phase 1 studies, approximately 4–5 mg of drug was released from the ring among women who reported continuous product use over a 28-day period [22, 23]. Because this analysis uses a continuous dapivirine release rate exposure variable, we used the point estimate at the midpoint of these values (4.5 mg/month) to assess risk reduction associated with Dapivirine Ring and Per-Sex-Act HIV Risk • JID 2024:229 (15 April) • 1159 D ow nloaded from https://academ ic.oup.com /jid/article/229/4/1158/7473606 by C ynthia W arren user on 07 O ctober 2024 consistent ring use. Use of the 4.5 mg/month midpoint allows for adequate comparison to previous evaluations of ring effica- cy that use categorical exposure variables. These studies define consistent ring use as >4.0 mg/month, which includes all dapi- virine release rates between 4 and 5 mg/month. Given that measurement of residual dapivirine in returned rings began a year into the study, we imputed monthly dapivirine release rates using a joint hidden Markov model (Supplementary Methods). Estimating Per-Sex-Act Risk Reduction Modeling the Sex Act Time Scale At quarterly visits, women were asked to provide information about their sexual behaviors, including the number of sexual partners they had in the past 3 months, whether they had a con- sistent primary partner over the past 3 months, the number of vaginal sex acts with their primary partner in the past week, and number of times a condom was used. Women were also asked about numbers of anal sex acts; however, only vaginal sex acts were considered in this analysis given that anal sex may have occurred at the same encounter and receptive anal intercourse was not found to be an independent risk factor for HIV-1 ac- quisition in prior analyses of ASPIRE participants [24]. To car- ry out our analysis on the per-sex-act scale, we required complete monthly sexual behavior data for participants across follow-up. To predict numbers of monthly sex acts, we mod- eled participant-reported sex acts in the past week using a mixed effects Poisson model. The model included participant- specific intercepts and slopes for the study visit month variable to allow for individual variation in sex acts at baseline and change in sex acts over time. We included as fixed effects base- line and time-varying covariates thought to be correlated with sexual behaviors based on our own hypotheses and the pub- lished literature, including study site, age, marital status, num- ber of live births, BV status, N. gonorrhoeae, C. trachomatis, and T. vaginalis infection, alcohol use, smoking status, having a pri- mary or new sexual partner, number of sexual partners, num- ber of sex acts at baseline, family planning use, and having any vaginal cleaning practices. A single fitted model was used to predict numbers of sex acts since the last monthly visit. Regression Models Models of per-sex-act risk reduction included women who were confirmed to be without HIV-1 at enrollment and had imputed sex acts and dapivirine release data across follow-up. Additionally, we excluded women from 2 study sites with lower product adherence and study retention that were discontinued early, as was done in a post hoc analysis for the ASPIRE trial. To model per-sex-act HIV-1 risk reduction associated with ring re- lease rates of 4.5 mg/month (ie, consistent ring use), we fit Cox re- gression models using the cumulative number of predicted sex acts between enrollment and first HIV-1 detection as the outcome. Given that tests for HIV-1 RNA were only conducted quarterly, the month when HIV-1 acquisition occurred was imputed using the same joint hidden Markov model used to impute monthly da- pivirine release rates (Supplementary Methods). Primary expo- sure variables for study group (dapivirine or placebo ring) and continuous ring release rate were included in the Cox models; the exponentiated linear combination of the coefficients of these 2 terms was used to obtain a parameter estimate analogous to a hazard ratio (HR), comparing the probability of HIV-1 infection at a particular number of cumulative sex acts between women in the dapivirine ring group with 4.5 mg/month drug release and women in the placebo ring group (for whom dapivirine release rate was 0 mg/month), assuming no HIV-1 infection up to that point. Percent RRR was calculated using the following formula: %RRR = (1 − HR) × 100. Women were censored at first pregnan- cy, first product hold >3 days, and loss to follow-up given likely changes in HIV-1 risk after these events. All models were stratified by study site. Multivariable models were adjusted for time-varying participant-reported condomless sex in the past 7 days and the fol- lowing baseline variables: age, education, marital status, BV status, N. gonorrhoeae, C. trachomati,s and T. vaginalis diagnosis, any new sexual partners, multiple sexual partners, number of sex acts in last 3 months, any reported condomless sex in last 7 days, alcohol use, partner HIV-1 status and knowledge of ring use, family planning method, and age-specific local male HIV-1 prevalence (assuming that women had partners who were in their age group). Model parameter estimates were calculated separately for each of the 20 imputed datasets and averaged; standard errors were pooled using Rubin’s rules to obtain 95% confidence inter- vals (CIs) and 2-sided P values. Given that women in our analysis were censored for reasons that may be related to the study outcome of HIV-1 acquisition, we further adjusted our models us- ing inverse probability of censoring weights (IPCWs) to account for potential selection bias due to informative censoring (Supplementary Methods). Subgroup analyses were carried out based on baseline age (<25 and ≥25 years), N. gonorrhoeae/C. trachomatis/T. vaginalis di- agnoses, BV status, and whether women reported bleeding in the pri- or month given that women may have less HIV-1 exposure while experiencing bleeding. All statistical analyses were carried out in R version 3.6.1 (R Core Team). RESULTS In ASPIRE, 2629 women were randomized to use of either the dapivirine (n = 1313) or placebo ring (n = 1316). Of those women, 3 were retrospectively discovered to have had acute HIV-1 infection at baseline and were excluded. An additional 12 women had no follow-up after the enrollment visit. For this analysis, 9 women who had a product hold before their first follow-up visit, 17 with missing data for variables used in pre- diction and Markov chain Monte Carlo (MCMC) models, and an additional 214 women from 2 sites with lower product 1160 • JID 2024:229 (15 April) • Stalter et al D ow nloaded from https://academ ic.oup.com /jid/article/229/4/1158/7473606 by C ynthia W arren user on 07 O ctober 2024 http://academic.oup.com/jid/article-lookup/doi/10.1093/infdis/jiad550#supplementary-data http://academic.oup.com/jid/article-lookup/doi/10.1093/infdis/jiad550#supplementary-data http://academic.oup.com/jid/article-lookup/doi/10.1093/infdis/jiad550#supplementary-data http://academic.oup.com/jid/article-lookup/doi/10.1093/infdis/jiad550#supplementary-data http://academic.oup.com/jid/article-lookup/doi/10.1093/infdis/jiad550#supplementary-data adherence and study retention were also excluded. Therefore, we included a total of 2374 women (1187 each in the dapivirine and placebo groups) in our analysis. Women in the placebo and dapivirine ring groups (regardless of estimated release rates) had comparable sociodemographic characteristics (Table 1). Women who were estimated to have demonstrated consistent ring use at least once during the trial (≥4.5 mg/month) reported a median of 15.0 sex acts in the last 3 months (interquartile range [IQR], 6.0–36.0) and 33.4% reported recent condomless sex. Depot medroxyprogesterone acetate was the most used contraceptive method (used by 40.1% of women) at enrollment among all participants, and most women experienced regular bleeding at screening (53.2%). In our mixed model to predict monthly sex acts, the standard deviation of the study month random effect term was 0.35. The median number of predicted sex acts per 28 days across follow-up was similar between women in the placebo and dapivirine ring groups (median, 8; IQR, 5–13 in both groups) and sexual Table 1. Baseline Participant Characteristics Characteristic Placebo Group (n = 1187) Dapivirine Group: No Months With Estimated Release Rate ≥4.5 mg/mo (n = 813) Dapivirine Group: at Least 1 Month With Estimated Release Rate ≥4.5 mg/mo (n = 374) Age, y, median (IQR) 26.0 (23.0–31.0) 27.0 (23.0–32.0) 26.0 (22.0–31.0) Country Malawi 136 (11.5) 103 (12.7) 29 (7.8) South Africa 592 (49.9) 373 (45.9) 220 (58.8) Uganda 126 (10.6) 100 (12.3) 27 (7.2) Zimbabwe 333 (28.1) 237 (29.2) 98 (26.2) Highest level of education None 11 (0.9) 10 (1.2) 1 (0.3) Primary, not complete 111 (9.4) 98 (12.1) 26 (7.0) Primary, complete 65 (5.5) 50 (6.2) 18 (4.8) Secondary, not complete 466 (39.3) 313 (38.5) 136 (36.4) Secondary, complete 462 (38.9) 311 (38.3) 155 (41.4) College or university 72 (6.1) 31 (3.8) 38 (10.2) Married 537 (45.2) 383 (47.1) 135 (36.1) No. of live births, median (IQR) 2.0 (1.0, 3.0) 2.0 (1.0, 3.0) 2.0 (1.0, 2.0) Has primary partner 1181 (99.5) 811 (99.8) 373 (99.7) Partner knows about ring use 779 (66.0) 530 (65.4) 238 (63.8) Partner is circumcised 508 (43.0) 331 (40.8) 161 (43.2) Partner HIV-1 status Positive 12 (1.0) 15 (1.8) 7 (1.9) Negative 650 (55.0) 429 (52.9) 198 (53.1) Don’t know 519 (43.9) 367 (45.3) 168 (45.0) Multiple sexual partners in the past 3 mo 211 (17.8) 135 (16.6) 57 (15.2) Any new partner in past 3 mo 34 (2.9) 28 (3.4) 16 (4.3) No. of sex acts in last 3 mo, median (IQR) 21.0 (8.0–36.0) 24.0 (10.0–40.0) 15.0 (6.0–36.0) No. of sex acts in last 7 d, median (IQR) 2.0 (1.0–3.0) 2.0 (1.0–4.0) 1.0 (0.0–3.0) Any condomless sex with partner in last 7 d 524 (44.1) 359 (44.2) 125 (33.4) Intrauterine device 159 (13.4) 128 (15.7) 32 (8.6) Oral pills 118 (9.9) 88 (10.8) 32 (8.6) Hormonal implant 238 (20.1) 194 (23.9) 62 (16.6) Depot medroxyprogesterone acetate 500 (42.1) 279 (34.3) 173 (46.3) Norethisterone enanthate 149 (12.6) 96 (11.8) 75 (20.1) Any menstrual bleeding in past 3 mo 926 (78.0) 656 (80.8) 276 (74.0) Any vaginal practices 771 (65.0) 533 (65.6) 219 (58.6) Usual bleeding pattern at screening Amenorrheic 254 (21.4) 147 (18.1) 99 (26.5) Irregular 301 (25.4) 194 (23.9) 95 (25.4) Regular 632 (53.2) 472 (58.1) 180 (48.1) Neisseria gonorrhoeae 48 (4.0) 39 (4.8) 14 (3.7) Chlamydia trachomatis 126 (10.6) 96 (11.8) 51 (13.6) Trichomonas vaginalis 82 (6.9) 60 (7.4) 21 (5.6) Bacterial vaginosis 472 (39.8) 379 (6.6) 1 (31.8) Data are No. (%) except where indicated. Abbreviation: IQR, interquartile range. Dapivirine Ring and Per-Sex-Act HIV Risk • JID 2024:229 (15 April) • 1161 D ow nloaded from https://academ ic.oup.com /jid/article/229/4/1158/7473606 by C ynthia W arren user on 07 O ctober 2024 behaviors gradually declined in frequency over time (Supplementary Figure 1A). Among women in the dapivirine ring group, the median estimated dapivirine release rate across the 20 posterior samples was 3.3 mg/28 days (IQR, 2.7–3.7) (dis- tribution of dapivirine release rates by study visit shown in Supplementary Figure 1B). The median estimated dapivirine re- lease rate was similar across categories of sex acts (Supplementary Figure 1C). Overall, women in the placebo group experienced an esti- mated 83 HIV-1 acquisition events over 231 637 predicted sex acts, for an incidence rate of 3.6 events per 10 000 acts (95% CI, 2.9–4.4) (Table 2). Women in the dapivirine group ex- perienced an estimated 54 HIV-1 acquisition events over 230 517 predicted sex acts, for an incidence rate of 2.3 events per 10 000 acts (95% CI, 1.8–3.1). Women in the dapivirine ring group demonstrating consis- tent ring use (estimated dapivirine release of 4.5 mg/28 days) had a 57% reduction in HIV-1 risk (95% CI, 20%–74%) relative to placebo in unadjusted models. In multivariable models ad- justing for time-varying report of any condomless sex and base- line variables for age, education, marital status, BV status, N. gonorrhoeae/C. trachomatis/T. vaginalis diagnoses, sexual behaviors, alcohol use, partner HIV-1 status and knowledge of ring use, family planning method, and local HIV-1 preva- lence for men within the same age group, release rates associat- ed with consistent ring use were associated with a 62% HIV-1 RRR (95% CI, 32%–79%) compared to placebo. Mean stabilized IPCW values were close to 1 (South Africa sites IPCW mean, 0.997 [range: 0.319–3.514]; non-South Africa sites IPCW mean, 0.995 [range: 0.505–10.550]). However, standardized mean differences of covariates between censored and uncensored women were similar after weighting, indicating possible inade- quate model specification (Supplementary Figure 3). In the adjust- ed model incorporating IPCWs, dapivirine release indicative of consistent ring use was associated with a 63% RRR (95% CI, 33%–80%). There was significant risk reduction with dapivirine re- lease rates as low as 1.3 mg/month, but risk reduction estimates were higher with greater dapivirine release (Figure 1). In subgroup analyses, estimated per-sex-act HIV-1 incidence was highest among women with detected N. gonorrhoeae (11.0 events per 10 000 acts in placebo group and 7.2 events per 10 000 acts in dapivirine group) and C. trachomatis (7.3 events Table 2. Per-Sex-Act HIV-1 Relative Risk Reduction Associated With Consistent Dapivirine Ring Use (Estimated Release of 4.5 mg/mo) Dapivirine Group: HIV-1 Events Per 10 000 Sex Acts (95% CI)a Placebo Group: HIV-1 Events Per 10 000 Sex Acts (95% CI) Unadjusted Model Adjusted Modelb Adjusted and Weighted Modelb,c Per-Sex-Act RRR, % (95% CI) P Per-Sex-Act RRR, % (95% CI) P Per-Sex-Act RRR, % (95% CI) P Interaction P Overall 2.3 (1.8–3.1) 3.6 (2.9–4.4) 57 (24–75) .004 62 (32–79) .001 63 (33–80) .001 … Baseline age <25 y (n = 886) 5.0 (3.5–6.9) 5.3 (3.9–7.3) 53 (0–77) .049 61 (16–82) .016 62 (17–82) .014 .844 ≥25 y (n = 1488) 1.1 (.7–1.8) 2.8 (2.0–3.7) 47 (−25 to 77) .148 54 (−20 to 82) .114 55 (−16 to 83) .096 Baseline STIs/BV N. gonorrhoeae not detected (n = 2273) 2.1 (1.6–2.8) 3.3 (2.6–4.2) 56 (19–76) .009 61 (27–79) .003 62 (29–80) .003 .683 N. gonorrhoeae detected (n = 101) 7.2 (2.9–14.9) 11.0 (5.0–20.8) 59 (−104 to 92) .277 72 (−67 to 95) .162 72 (−64 to 95) .159 C. trachomatis not detected (n = 2101) 1.9 (1.3–2.6) 3.2 (2.5–4.1) 49 (3–73) .039 53 (9–76) .026 54 (10–77) .023 .181 C. trachomatis detected (n = 273) 6.2 (3.5–10.2) 7.3 (4.2–11.9) 75 (2–92) .020 81 (37–95) .007 83 (42–95) .005 T. vaginalis detected (n = 2211) 2.1 (1.6–2.9) 3.5 (2.7–4.3) 62 (30–80) .002 66 (35–83) .001 68 (38–83) .001 .250 T. vaginalis detected (n = 163) 4.9 (2.1–9.7) 5.2 (2.2–10.2) −26 (−621 to 78) .798 16 (−348 to 84) .839 10 (−363 to 83) .899 BV not detected (n = 1404) 2.0 (1.4–2.9) 2.7 (1.9–3.7) 51 (−6 to 77) .071 53 (−1 to 78) .052 54 (1 to 78) .048 .441 BV detected (n = 970) 2.8 (1.8–4.1) 5.0 (3.6–6.7) 63 (10–84) .028 71 (26–89) .010 72 (28–89) .008 Menses/bleeding in past mo No 2.9 (2.0–3.9) 4.0 (3.0–5.2) 47 (0–72) .049 55 (12–77) .020 56 (14–78) .017 .282 Yes 1.6 (.9–2.7) 2.9 (1.9–4.2) 77 (26–93) .014 78 (28–94) .013 79 (30–94) .011 All models were stratified by study site. RRR calculated as ( − hazard ratio) × 100. Abbreviations: BV, bacterial vaginosis; CI, confidence interval; HIV-1, human immunodeficiency virus-1; RRR, relative risk reduction; STI, sexually transmitted infection. aCrude incidence rates of HIV-1 events per 10 000 sex acts include all participants in the dapivirine ring group. However, the per-sex-act RRR estimates in the table compare the probability of HIV-1 infection between women in the dapivirine ring group with 4.5 mg/month drug release and women in the placebo ring group (for whom dapivirine release rate was 0 mg/month). Hence, comparison of the crude incidence rates will not equate to the unadjusted RRR estimate. bMultivariable Cox regression models were adjusted for report of any condomless sex and the following baseline variables: age, education, marital status, BV status, Chlamydia trachomatis, Neisseria gonorrhoeae, and Trichomonas vaginalis diagnosis, any new sexual partners, multiple sexual partners, number of sex acts in last 3 months, any condomless sex in last 7 days, alcohol use, partner HIV-1 status and knowledge of ring use, family planning method, and local HIV-1 prevalence for men within the same age group. cAdjusted using inverse probability of censoring weights to account for selection bias due to participant censoring at first pregnancy, first product hold >3 days, and loss-to-follow-up given likely changes in HIV-1 risk after these events. 1162 • JID 2024:229 (15 April) • Stalter et al D ow nloaded from https://academ ic.oup.com /jid/article/229/4/1158/7473606 by C ynthia W arren user on 07 O ctober 2024 http://academic.oup.com/jid/article-lookup/doi/10.1093/infdis/jiad550#supplementary-data http://academic.oup.com/jid/article-lookup/doi/10.1093/infdis/jiad550#supplementary-data http://academic.oup.com/jid/article-lookup/doi/10.1093/infdis/jiad550#supplementary-data http://academic.oup.com/jid/article-lookup/doi/10.1093/infdis/jiad550#supplementary-data http://academic.oup.com/jid/article-lookup/doi/10.1093/infdis/jiad550#supplementary-data per 10 000 acts in placebo group vs 6.2 events per 10 000 acts in dapivirine group) at enrollment. However, RRR estimates did not differ between women with or without N. gonorrhoeae and C. trachomatis infection at enrollment according to interaction models (P = .683 and P = .181, respectively). Additionally, no sig- nificant difference in RRR was identified between age, BV status, and T. vaginalis detection subgroups. In our interaction model based on time-varying experience of bleeding in the past month, risk reduction estimates were higher for months when bleeding was reported versus when not reported (Supplementary Figure 2), but this difference was not statistically significant (P = .282). DISCUSSION In this secondary analysis of data from the ASPIRE trial, we conducted a rigorous evaluation of HIV-1 risk reduction asso- ciated with use of the dapivirine vaginal ring with a more com- plete accounting for women’s sexual behaviors. Unlike other analyses that evaluate HIV-1 risk reduction on a time scale, as- sessing risk reduction on the sex act scale may better control for the heterogeneity in women’s sexual behaviors and ensure that accumulation of HIV-1 risk is directly tied to potential expo- sure. We demonstrated a positive relationship between rate of drug release from the dapivirine vaginal ring and HIV-1 risk reduction. Further, dapivirine release rates indicative of consistent ring use were associated with an estimated 63% re- duction in per-sex-act HIV-1 risk after adjusting for other po- tential confounders and accounting for informative censoring using IPCWs. Dapivirine release rates were imputed in our analysis using MCMC methods to account for missingness and measurement error in observed ring release measures. In our previous analy- sis using all available measured ring release data, which exclud- ed 46 women with HIV-1 end points that occurred prior to collection of used rings for dapivirine quantification, we dem- onstrated a 43% risk reduction associated with dapivirine re- lease rates consistent with continuous use [20]. In this previous analysis, the same levels of dapivirine release were as- sociated with a 71% HIV-1 risk reduction when starting follow- up at 12 months to create a common start time; however, as this was a secondary analysis that excluded an additional 54 HIV-1 end points and 1436 woman-years of follow-up, it is possible this estimate was biased due to missing data from early study visits. Here, our ability to use the full range of study follow-up data due to our imputation methods allows us to correct for se- lection bias due to previous exclusion of these end points. We observed little change in HIV-1 risk reduction estimates when models were weighted using IPCWs. This was also observed in previous work utilizing IPCWs to evaluate the efficacy of oral PrEP, which censored participants at first missed visit and detec- tion of poor adherence [19]. Estimating unbiased IPCWs is de- pendent correct model specification [25, 26] and inclusion of all variables associated with time to censoring and time to failure. Therefore, this small change could be due to poor weight model specification and might suggest our models exclude other unmea- sured predictors of censoring. This is supported by our IPCW di- agnostics that showed similar covariate balance between censored and uncensored before and after weighting. Other potential limitations of our analysis should be consid- ered. First, predicted numbers of monthly sex acts were based on women’s self-reported sex acts in the prior week. Such data are subject to recall bias (particularly among women who have frequent sex) and social desirability bias. Additionally, given that estimated values (ie, predicted sex acts and IPCWs) are treated as fixed quantities in the Cox regression models, the pooled standard errors used to estimate per-sex-act HIV risk re- duction may not fully reflect the variability in these data. Second, per-sex-act risk depends largely on the HIV-1 status of their partner. However, <2% of women reported that their primary partner was living with HIV-1 at baseline while nearly half of women did not know their partner’s status. We also adjusted for age-specific local HIV-1 prevalence among men to further account for partner HIV-1 status and variation in women’s HIV-1 exposure, but this is an imperfect proxy for confirmation of women’s partner status. As a result, per-act incidence calcu- lated in our analysis is likely an underestimate of the per-act in- cidence of women who are HIV-exposed. Our analysis supports the use of the dapivirine ring as an effica- cious HIV-1 prevention product for women. While the efficacy of the ring for preventing male-to-female HIV-1 transmission via vaginal sex is not as high as the efficacy of daily PrEP or consistent Figure 1. Per-sex-act HIV-1 risk reduction with incremental dapivirine release rates. Solid line indicates percent relative risk reduction estimate. Shaded area in- dicates 95% confidence interval. Dapivirine Ring and Per-Sex-Act HIV Risk • JID 2024:229 (15 April) • 1163 D ow nloaded from https://academ ic.oup.com /jid/article/229/4/1158/7473606 by C ynthia W arren user on 07 O ctober 2024 http://academic.oup.com/jid/article-lookup/doi/10.1093/infdis/jiad550#supplementary-data http://academic.oup.com/jid/article-lookup/doi/10.1093/infdis/jiad550#supplementary-data condom use, both of which reduce the risk of HIV transmission via multiple routes and are associated with >90% risk reduction [17, 27], the ring has important characteristics that may suit some women’s needs (eg, longer duration, less user-dependent, allows for discreet use, potentially fewer side effects, and high acceptability [28]). Therefore, communication of risk associated with the ring rel- ative to other PrEP options should be part of a person-centered ap- proach, acknowledging that women are in the best position to decide which option is best for their individual situation [29]. As ad- ditional HIV-1 prevention products emerge from the development pipeline, including multipurpose prevention technologies, we en- courage similar analyses to evaluate risk reduction associated with product exposure as a complement to intention-to-treat analysis as an approach to best understand product efficacy. Supplementary Data Supplementary materials are available at The Journal of Infectious Diseases online (http://jid.oxfordjournals.org/). Supplementary materials consist of data provided by the author that are published to benefit the reader. The posted materials are not copyedited. The contents of all supplementary data are the sole responsibility of the authors. Questions or messages regarding errors should be addressed to the author. Notes Study team leadership. Jared Baeten, University of Washington (Protocol Chair); Thesla Palanee-Phillips, Wits Reproductive Health and HIV Institute (Protocol Cochair); Elizabeth Brown, Fred Hutchinson Cancer Research Center (Protocol Statistician); Lydia Soto-Torres, US National Institute of Allergy and Infectious Diseases (Medical Officer); and Katie Schwartz, FHI 360 (Clinical Research Manager). Study sites and site investigators of record. Malawi, Blantyre site (Johns Hopkins University, Queen Elizabeth Hospital), Bonus Makanani; Malawi, Lilongwe site (University of North Carolina, Chapel Hill), Francis Martinson; South Africa, Cape Town site (University of Cape Town), Linda-Gail Bekker; South Africa, Durban-Botha’s Hill, Chatsworth, Isipingo, Tongaat, Umkomaas, Verulam sites (South African Medical Research Council), Vaneshree Govender, Samantha Siva, Zakir Gaffoor, Logashvari Naidoo, Arendevi Pather, and Nitesha Jeenarain; South Africa, Durban, eThekwini site (Center for the AIDS Programme for Research in South Africa), Gonasagrie Nair; South Africa, Johannesburg site (Wits RHI), Thesla Palanee-Phillips; Uganda, Kampala site (John Hopkins University, Makerere University), Flavia Matovu Kiweewa; Zimbabwe, Chitungwiza, Seke South and Zengeza sites (University of Zimbabwe Clinical Trials Research Centre), Nyaradzo Mgodi; Zimbabwe, Harare, Spilhaus site (University of Zimbabwe Clinical Trials Research Centre), Felix Mhlanga. Author contributions. R. M. S., J. M. B., and E. R. B. concep- tualized the primary research question and overall study design. R. M. S. led the data analyses. T. Q. D. and E. R. B. con- tributed to the data analyses and provided statistical guidance. C. W. H., T. P. P., A. v. d. S., S. L. H., F. M. K., N. M. M., M. A. M., L. G. B., L. S. T., J. M. B., and E. R. B. led parts of or directly contributed to implementation and data collection for the parent study (MTN-020/ASPIRE). R. M. S. drafted the initial manuscript, and all authors contrib- uted to results interpretation and manuscript revisions. All au- thors have read and approved the manuscript. Acknowledgments. We thank all the women who participated in MTN-020/ASPIRE. Data management was provided by The Statistical Center for HIV/AIDS Research and Prevention (Fred Hutchinson Cancer Research Center, Seattle, WA) and site laboratory oversight was provided by the Microbicide Trials Network Laboratory Center (Pittsburgh, PA). The vaginal rings used in this study were developed and supplied by the International Partnership for Microbicides. The study was de- signed and implemented by the Microbicide Trials Network. Disclaimer. The content is solely the responsibility of the au- thors and does not necessarily represent the official views of the National Institutes of Health. Financial support. This work was supported by the National Institute of Allergy and Infectious Diseases, National Institutes of Health (NIH) (grant numbers UM1AI068633, UM1AI068615, and UM1AI106707); with cofunding from the Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH and the National Institute of Mental Health, NIH. R. M. S. was supported by an NIH institu- tional training grant (grant number T32AI007140). Potential conflicts of interest. C. W. H. has received grant sup- port from Merck and Gilead Sciences; is a co-inventer of two is- sued U.S. patents related to microbicides; and is founder of Prionde BioPharma, LLC, a microbicide company. T. P. P. has received grant support from Gilead Sciences, MSD, and the South African Medical Research Council; and participates on advisory boards for the Dual Protection Pill (DPP) Consortium and the Maximizing Options to Advance Informed Choice for HIV Prevention (MOSAIC) project. A. D. S. has received consult- ing fees from the Magee Women’s Research Institute. S. L. H. has received consulting fees from Merck. M. M. has received grant support from ViiV Healthcare, GSK, and Gilead Sciences; royalties from Elsevier; and consulting fees and honoraria from Bio-Rad. L. G. B. has received honoraria from ViiV Healthcare, Gilead Sciences and Merck Pty Ltd. J. M. B. is an employee of Gilead Sciences, out- side the present work. E. R. B. has received payment for participation on Data Safety Monitoring Boards for Merck and the Adolescent Trials Network and is a paid statistical editor for JID. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consid- er relevant to the content of the manuscript have been disclosed. 1164 • JID 2024:229 (15 April) • Stalter et al D ow nloaded from https://academ ic.oup.com /jid/article/229/4/1158/7473606 by C ynthia W arren user on 07 O ctober 2024 http://academic.oup.com/jid/article-lookup/doi/10.1093/infdis/jiad550#supplementary-data http://jid.oxfordjournals.org/ http://academic.oup.com/jid/article-lookup/doi/10.1093/infdis/jiad550#supplementary-data http://academic.oup.com/jid/article-lookup/doi/10.1093/infdis/jiad550#supplementary-data References 1. UNAIDS. Fact sheet—latest global and regional statistics on the status of the AIDS epidemic. Geneva: UNAIDS, 2020. 2. Celum C, Baeten J. PrEP for HIV prevention: evidence, global scale-up, and emerging options. Cell Host Microbe 2020; 27:502–6. 3. Marrazzo JM, Ramjee G, Richardson BA, et al. Tenofovir-based preexposure prophylaxis for HIV infection among African women. N Engl J Med 2015; 372:509–18. 4. Van Damme L, Corneli A, Ahmed K, et al. Preexposure prophylaxis for HIV infection among African women. N Engl J Med 2012; 367:411–22. 5. Celum C, Hosek S, Tsholwana M, et al. PrEP uptake, per- sistence, adherence, and effect of retrospective drug level feedback on PrEP adherence among young women in Southern Africa: results from HPTN 082, a randomized controlled trial. PLoS Med 2021; 18:e1003670. 6. Baeten JM, Palanee-Phillips T, Brown ER, et al. Use of a vaginal ring containing dapivirine for HIV-1 prevention in women. N Engl J Med 2016; 375:2121–32. 7. Nel A, van Niekerk N, Kapiga S, et al. Safety and efficacy of a dapivirine vaginal ring for HIV prevention in women. N Engl J Med 2016; 375:2133–43. 8. International Partnership for Microbicides (IPM). IPM’s dapivirine ring for women’s HIV prevention receives WHO prequalification. Silver Spring, MD: IPM, 2020. 9. International Partnership for Microbicides (IPM). In mile- stone for women’s HIV prevention, European medicines agency adopts positive opinion on monthly vaginal ring to reduce HIV risk. Silver Spring, MD: IPM, 2020. 10. International Partnership for Microbicides (IPM). IPM welcomes WHO’s recommendation for dapivirine vaginal ring as new women’s HIV prevention option. Silver Spring, MD: IPM, 2021. 11. World Health Organization (WHO). WHO recommends the dapivirine vaginal ring as a new choice for HIV preven- tion for women at substantial risk of HIV infection. Geneva: WHO, 2021. 12. International Partnership for Microbicides (IPM). South Africa approves dapivirine vaginal ring for use by women. Silver Spring, MD: IPM, 2022. 13. Gwarisa M. Dapivirine, vaginal ring approved for use in Zimbabwe. Harare: Health Times, 14 July, 2021. 14. AVAC. Country planning for product introduction matrix. https://www.prepwatch.org/resources/product-introduction- country-planning-matrix/. Accessed 5 November 2023. 15. Baeten JM, Donnell D, Ndase P, et al. Antiretroviral pro- phylaxis for HIV prevention in heterosexual men and women. N Engl J Med 2012; 367:399–410. 16. Thigpen MC, Kebaabetswe PM, Paxton LA, et al. Antiretroviral preexposure prophylaxis for heterosexual HIV transmission in Botswana. N Engl J Med 2012; 367:423–34. 17. Donnell D, Baeten JM, Bumpus NN, et al. HIV protective efficacy and correlates of tenofovir blood concentrations in a clinical trial of PrEP for HIV prevention. J Acquir Immune Defic Syndr 2014; 66:340. 18. Anderson PL, Glidden DV, Liu A, et al. Emtricitabine-tenofovir concentrations and pre-exposure prophylaxis efficacy in men who have sex with men. Sci Transl Med 2012; 4:151ra125. 19. Murnane PM, Brown ER, Donnell D, et al. Estimating efficacy in a randomized trial with product nonadherence: application of multiple methods to a trial of preexposure prophylaxis for HIV prevention. Am J Epidemiol 2015; 182:848–56. 20. Brown ER, Hendrix CW, van der Straten A, et al. Greater dapivirine release from the dapivirine vaginal ring is corre- lated with lower risk of HIV-1 acquisition: a secondary analysis from a randomized, placebo-controlled trial. J Int AIDS Soc 2020; 23:e25634. 21. Seserko LA, Emory JF, Hendrix CW, Marzinke MA. The development and validation of an UHPLC-MS/MS method for the rapid quantification of the antiretroviral agent dapi- virine in human plasma. Bioanalysis 2013; 5:2771–83. 22. Chen BA, Panther L, Marzinke MA, et al. Phase 1 safety, pharmacokinetics, and pharmacodynamics of dapivirine and maraviroc vaginal rings: a double-blind randomized trial. J Acquir Immune Defic Syndr 2015; 70:242–9. 23. Nel A, Bekker LG, Bukusi E, et al. Safety, acceptability and adherence of dapivirine vaginal ring in a microbicide clin- ical trial conducted in multiple countries in sub-Saharan Africa. PLoS One 2016; 11:e0147743. 24. Peebles K, van der Straten A, Palanee-Phillips T, et al. Brief report: anal intercourse, HIV-1 risk, and efficacy in a trial of a dapivirine vaginal ring for HIV-1 prevention. J Acquir Immune Defic Syndr 2020; 83:197–201. 25. Howe CJ, Cole SR, Chmiel JS, Munoz A. Limitation of in- verse probability-of-censoring weights in estimating sur- vival in the presence of strong selection bias. Am J Epidemiol 2011; 173:569–77. 26. Howe CJ, Cole SR, Lau B, Napravnik S, Eron JJ Jr. Selection bias due to loss to follow up in cohort studies. Epidemiology 2016; 27:91. 27. Pinkerton SD, Abramson PR. Effectiveness of condoms in preventing HIV transmission. Soc Sci Med 1997; 44:1303–12. 28. van der Straten A, Agot K, Ahmed K, et al. The Tablets, Ring, Injections as Options (TRIO) study: what young African women chose and used for future HIV and pregnancy prevention. J Int AIDS Soc 2018; 21:e25094. 29. Pantelic M, Stegling C, Shackleton S, Restoy E. Power to participants: a call for person-centred HIV prevention ser- vices and research. J Int AIDS Soc 2018; 21:e25167. Dapivirine Ring and Per-Sex-Act HIV Risk • JID 2024:229 (15 April) • 1165 D ow nloaded from https://academ ic.oup.com /jid/article/229/4/1158/7473606 by C ynthia W arren user on 07 O ctober 2024 https://www.prepwatch.org/resources/product-introduction-country-planning-matrix/ https://www.prepwatch.org/resources/product-introduction-country-planning-matrix/ Assessing Per-Sex-Act HIV-1 Risk Reduction Among Women Using the Dapivirine Vaginal Ring METHODS Study Population and Procedures Survey and Laboratory Measures Adherence Measures Estimating Per-Sex-Act Risk Reduction Modeling the Sex Act Time Scale Regression Models RESULTS DISCUSSION Supplementary Data Notes References