Estimating efficacy in a randomized trial with product nonadherence: application of multiple methods to a trial of preexposure prophylaxis for HIV prevention

Assessing Per-Sex-Act HIV-1 Risk Reduction Among Women Using the Dapivirine Vaginal Ring

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.

Preexposure Prophylaxis for the Prevention of HIV: Updated Evidence Report and Systematic Review for the US Preventive Services Task Force

Importance

A 2019 review for the US Preventive Services Task Force (USPSTF) found oral preexposure prophylaxis (PrEP) associated with decreased HIV infection risk vs placebo or no PrEP in adults at increased HIV acquisition risk. Newer PrEP regimens are available.

Objective

To update the 2019 review on PrEP, to inform the USPSTF.

Data Sources

Ovid MEDLINE, Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials, and Embase (January 2018 to May 16, 2022); surveillance through March 24, 2023.

Study Selection

Randomized clinical trials of PrEP vs placebo or no PrEP or newer vs older PrEP regimens and diagnostic accuracy studies of instruments for predicting incident HIV infection.

Data Extraction and Synthesis

Dual review of titles and abstracts, full-text articles, study quality, and data abstraction. Data were pooled using the DerSimonian and Laird random-effects model.

Main Outcomes and Measures

HIV acquisition, mortality, and harms; and diagnostic test accuracy.

Results

Thirty-two studies were included in the review (20 randomized clinical trials [N = 36 543] and 12 studies of diagnostic accuracy [N = 5 544 500]). Eleven trials in the 2019 review found oral PrEP associated with decreased HIV infection risk vs placebo or no PrEP (n = 18 172; relative risk [RR], 0.46 [95% CI, 0.33-0.66]). Higher adherence was associated with greater efficacy. One new trial (n = 5335) found oral tenofovir alafenamide/emtricitabine (TAF/FTC) to be noninferior to tenofovir disoproxil fumarate/emtricitabine (TDF/FTC) in men who have sex with men (RR, 0.47 [95% CI, 0.19-1.14]). Two new trials found long-acting injectable cabotegravir associated with decreased risk of HIV infection vs oral TDF/FTC (RR, 0.33 [95% CI, 0.18-0.62] in cisgender men who have sex with men and transgender women [n = 4490] and RR, 0.11 [95% CI, 0.04-0.31] in cisgender women [n = 3178]). Discrimination of instruments for predicting incident HIV infection was moderate in men who have sex with men (5 studies; n = 25 488) and moderate to high in general populations of persons without HIV (2 studies; n = 5 477 291).

Conclusions and Relevance

In adults at increased HIV acquisition risk, oral PrEP was associated with decreased risk of acquiring HIV infection compared with placebo or no PrEP. Oral TAF/FTC was noninferior to oral TDF/FTC, and injectable cabotegravir reduced the risk of HIV infection compared with oral TDF/FTC in the populations studied.

Advancing considerations of context in the evaluation and implementation of evidence-based biomedical HIV prevention interventions: a review of recent research

PURPOSE OF REVIEW

A paradigm shift is needed in how we think about biomedical HIV prevention product effectiveness. Often, we expect randomized trial findings to be generalizable across populations and settings where products will be delivered, without consideration of key contextual drivers that could impact effectiveness. Moreover, researchers and policy-makers generally discount products with varied effect sizes across contexts, rather than explicating the drivers of these differences and using them to inform equitable product choice and delivery. We conducted a review of the recent HIV prevention research to advance considerations of context in choices of when, why, and how to implement biomedical HIV prevention products, with a particular focus on daily oral preexposure prophylaxis (PrEP) and the dapivirine vaginal ring (DPV).

RECENT FINDINGS

Findings across recent studies of PrEP and DPV emphasize that products that do not work well in one context might be highly desirable in another. Key contextual drivers of PrEP and DPV effectiveness, use, and implementation include population, health system, cultural, and historical factors. We recommend conceptualization, measurement, and analysis approaches to fully understand the potential impact of context on prevention product delivery. Execution of these approaches has real-world implications for HIV prevention product choice and could prevent the field from dismissing biomedical HIV prevention products based on trial findings alone.

SUMMARY

Ending the HIV epidemic will require tailored, person-centered, and equitable approaches to design, implement, and evaluate HIV prevention products which necessitates considerations of context in ongoing research and implementation.

Use of Machine Learning to Estimate the Per-Protocol Effect of Low-Dose Aspirin on Pregnancy Outcomes: A Secondary Analysis of a Randomized Clinical Trial

IMPORTANCE

In randomized clinical trials (RCTs), per-protocol effects may be of interest in the presence of nonadherence with the randomized treatment protocol. Using machine learning in per-protocol effect estimation can help avoid model misspecification owing to strong parametric assumptions, as is common with standard methods (eg, logistic regression).

OBJECTIVES

To demonstrate the use of ensemble machine learning with augmented inverse probability weighting (AIPW) for per-protocol effect estimation in RCTs and to evaluate the per-protocol effect size of aspirin on pregnancy.

DESIGN, SETTING, AND PARTICIPANTS

This secondary analysis used data from 1227 women in the Effects of Aspirin in Gestation and Reproduction (EAGeR) trial, a multicenter, block-randomized, double-blind, placebo-controlled clinical trial of the effect of daily low-dose aspirin on pregnancy outcomes in women at high risk of pregnancy loss. Participants were recruited at 4 university medical centers in the US from June 15, 2007, to July 15, 2012. Women were followed up for 6 menstrual cycles for attempted pregnancy and 36 weeks of gestation if pregnancy occurred. Follow-up was completed on August 17, 2012. Data analyses were performed on July 9, 2021.

EXPOSURES

Daily low-dose (81 mg) aspirin taken at least 5 of 7 days per week for at least 80% of follow-up time relative to placebo.

MAIN OUTCOMES AND MEASURES

Pregnancy detected using human chorionic gonadotropin (hCG) levels.

RESULTS

Among the 1227 women included in the analysis (mean SD age, 28.74 [4.80] years), 1161 (94.6%) were non-Hispanic White and 858 (69.9%) adhered to the protocol. Five machine learning models were combined into 1 meta-algorithm, which was used to construct an AIPW estimator for the per-protocol effect. Compared with adhering to placebo, adherence to the daily low-dose aspirin protocol for at least 5 of 7 days per week was associated with an increase in the probability of hCG-detected pregnancy of 8.0 (95% CI, 2.5-13.6) more hCG-detected pregnancies per 100 women in the sample, which is substantially larger than the estimated intention-to-treat estimate of 4.3 (95% CI, -1.1 to 9.6) more hCG-detected pregnancies per 100 women in the sample.

CONCLUSIONS AND RELEVANCE

These findings suggest that a low-dose aspirin protocol is associated with increased hCG-detected pregnancy in women who adhere to treatment for at least 5 days per week. With the presence of nonadherence, per-protocol treatment effect estimates differ from intention-to-treat estimates in the EAGeR trial. The results of this secondary analysis of clinical trial data suggest that machine learning could be used to estimate per-protocol effects by adjusting for confounders related to nonadherence in a more flexible way than traditional regressions.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT00467363.

Perceived HIV Acquisition Risk and Low Uptake of PrEP Among a Cohort of Transgender Women With PrEP Indication in the Eastern and Southern United States

INTRODUCTION

Preexposure prophylaxis (PrEP) is effective in preventing HIV among adherent users. However, PrEP uptake among transgender women is low, and current prescribing guidelines from the Centers for Disease Control and Prevention (CDC) are not specific to transgender women. Self-perceived risk of HIV among those who are PrEP-indicated is not well understood.

METHODS

This cross-sectional analysis included 1293 transgender women screened at baseline from March 2018 to May 2020 for a multisite, prospective cohort study. We compared the prevalence of PrEP indication using current CDC prescribing criteria versus transgender women-specific criteria developed by study investigators with community input. We identified factors associated with study-specific PrEP indication and factors associated with self-perceived low to no HIV risk among those who were PrEP-indicated. We also calculated descriptive statistics to depict the PrEP care continuum.

RESULTS

PrEP indication prevalence using transgender women-specific criteria was 47% (611), 155 more than who were identified using the CDC criteria. Eighty-three percent were aware of PrEP, among whom 38% had ever used PrEP. Among PrEP ever users, 63% were using PrEP at the time of the study. There were 66% of current PrEP users who reported 100% adherence within the previous 7 days. Among those who were PrEP-indicated, 13% were using and adherent to PrEP at the time of the study. More than half (55%) of PrEP-indicated participants had low or no self-perceived HIV risk.

CONCLUSIONS

These findings suggest that further guidance is needed for health care providers in prescribing PrEP to transgender women. Greater uptake and adherence are also needed for optimal effectiveness.

Perceived HIV Acquisition Risk and Low Uptake of PrEP Among a Cohort of Transgender Women With PrEP Indication in the Eastern and Southern United States

INTRODUCTION

Preexposure prophylaxis (PrEP) is effective in preventing HIV among adherent users. However, PrEP uptake among transgender women is low, and current prescribing guidelines from the Centers for Disease Control and Prevention (CDC) are not specific to transgender women. Self-perceived risk of HIV among those who are PrEP-indicated is not well understood.

METHODS

This cross-sectional analysis included 1293 transgender women screened at baseline from March 2018 to May 2020 for a multisite, prospective cohort study. We compared the prevalence of PrEP indication using current CDC prescribing criteria versus transgender women-specific criteria developed by study investigators with community input. We identified factors associated with study-specific PrEP indication and factors associated with self-perceived low to no HIV risk among those who were PrEP-indicated. We also calculated descriptive statistics to depict the PrEP care continuum.

RESULTS

PrEP indication prevalence using transgender women-specific criteria was 47% (611), 155 more than who were identified using the CDC criteria. Eighty-three percent were aware of PrEP, among whom 38% had ever used PrEP. Among PrEP ever users, 63% were using PrEP at the time of the study. There were 66% of current PrEP users who reported 100% adherence within the previous 7 days. Among those who were PrEP-indicated, 13% were using and adherent to PrEP at the time of the study. More than half (55%) of PrEP-indicated participants had low or no self-perceived HIV risk.

CONCLUSIONS

These findings suggest that further guidance is needed for health care providers in prescribing PrEP to transgender women. Greater uptake and adherence are also needed for optimal effectiveness.

Low costs and opportunities for efficiency: a cost analysis of the first year of programmatic PrEP delivery in Kenya's public sector

Background

In 2017, the Kenyan Ministry of Health integrated provision of pre-exposure prophylaxis (PrEP) into public HIV-1 care clinics as a key component of the national HIV-1 prevention strategy. Estimates of the cost of PrEP provision are needed to inform the affordability and cost-effectiveness of PrEP in Kenya.

Methods

We conducted activity-based micro-costing from the payer perspective to estimate both the financial and economic costs of all resources and activities required to provide PrEP in Kenya’s public sector. We estimated total and unit costs in 2019 United States dollars from a combination of project expense reports, Ministry of Health training reports, clinic staff interviews, time-and-motion observations, and routinely collected data from PrEP recipient files from 25 high-volume HIV-1 care clinics.

Results

In the first year of programmatic PrEP delivery in 25 HIV-1 care clinics, 2,567 persons initiated PrEP and accrued 8,847 total months of PrEP coverage, accounting for 2 % of total outpatient clinic visits. The total financial cost to the Ministry of Health was $91,175, translating to an average of $10.31 per person per month. The majority (69 %) of financial costs were attributable to PrEP medication, followed by administrative supplies (17 %) and training (9 %). Economic costs were higher ($188,584 total; $21.32 per person per month) due to the inclusion of the opportunity cost of staff time re-allocated to provide PrEP and a proportional fraction of facility overhead. The vast majority (88 %) of the annual $80,811 economic cost of personnel time was incurred during activities to recruit new clients (e.g., discussion of PrEP within HIV-1 testing and counselling services), while the remaining 12 % was for activities related to both initiation and maintenance of PrEP provision (e.g., client consultations, technical advising, support groups).

Conclusions

Integration of PrEP provision into existing public health HIV-1 care service delivery platforms resulted in minimal additional staff burden and low incremental costs. Efforts to improve the efficiency of PrEP provision should focus on reductions in the cost of PrEP medication and extra-clinic demand creation and community sensitization to reduce personnel time dedicated to recruitment-related activities.

Trial registration

ClinicalTrials.gov registration NCT03052010. Retrospectively registered on February 14, 2017.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12913-021-06832-3.

Evaluation of the Safety, Acceptability, and Pharmacokinetic Profile of a Gel Formulation of OB-002 in Healthy Volunteers

OB-002 is an extremely potent CCR5 antagonist that has previously been shown to completely block transmission in a nonhuman primate model of HIV infection. The purpose of this study was to characterize the safety, acceptability, and pharmacokinetic profile of a gel formulation of OB-002 (OB-002H). The trial had two phases, an open label single dose exposure (vaginal and rectal) and a randomized placebo controlled multiple dose phase during which study participants received five vaginal daily doses of OB-002H gel or matched placebo in a 2:1 ratio. Serum OB-002 levels were quantified at multiple time points up to 24 h after the first dose. A total of thirty female and male participants were enrolled in the study (12 in the single dose phase and 18 in the multiple dose phase). All adverse events were Grade 1 or 2, and the majority was unrelated to study product. Only two product-related transient Grade 2 events (both vulval dryness) occurred in the study, both in the OB-002H gel randomized multiple dose arm. All colposcopic and anoscopic assessments following product exposure were normal. There was no evidence of systemic absorption of OB-002. Overall, the product had a positive acceptability profile, and most study participants would consider using the product for protection against HIV or pregnancy. Future studies are needed to assess the extended safety and acceptability of OB-002H gel in sexually active participants. Clinical Trial Registration Number: NCT04791007.

Age-Specific Risk Scores Do Not Improve HIV-1 Prediction Among Women in South Africa

Supplemental Digital Content is Available in the Text.

HIV-1 risk scoring tools could help target provision of prevention modalities such as pre-exposure prophylaxis. Recent research suggests that risk scores for women aged 18–45 may not predict risk well among young women aged 18–24. We evaluated the predictive performance of age-specific risk scores compared with the existing non–age-specific VOICE risk score, developed for women aged 18–45.

Recommendations for Increasing Physician Provision of Pre-Exposure Prophylaxis: Implications for Medical Student Training

There is growing evidence that pre-exposure prophylaxis (PrEP) prevents HIV acquisition. However, in the United States, approximately only 4% of people who could benefit from PrEP are currently receiving it, and it is estimated only 1 in 5 physicians has ever prescribed PrEP. We conducted a scoping review to gain an understanding of physician-identified barriers to PrEP provision. Four overarching barriers presented in the literature: Purview Paradox, Patient Financial Constraints, Risk Compensation, and Concern for ART Resistance. Considering the physician-identified barriers, we make recommendations for how physicians and students may work to increase PrEP knowledge and competence along each stage of the PrEP cascade. We recommend adopting HIV risk assessment as a standard of care, improving physician ability to identify PrEP candidates, improving physician interest and ability in encouraging PrEP uptake, and increasing utilization of continuous care management to ensure retention and adherence to PrEP.

Metabolomic basis for response to high dose vitamin D in critical illness

BACKGROUND & AIMS

It is unclear if intervention can mitigate the dramatic alterations of metabolic homeostasis present in critical illness. Our objective was to determine the associations between increased 25-hydroxyvitamin D levels following high dose vitamin D₃ and more favorable metabolomic profiles in critical illness.

METHODS

We performed a post-hoc metabolomics study of the VITdAL-ICU randomized double-blind, placebo-controlled trial. Trial patients from Medical and Surgical Intensive Care Units at a tertiary university hospital with 25-hydroxyvitamin D level ≤20 ng/mL received either high dose oral vitamin D₃ (540,000 IU) or placebo. We performed an analysis of 578 metabolites from 1215 plasma samples from 428 subjects at randomization (day 0), day 3 and 7. Using mixed-effects modeling, we studied changes in metabolite profiles in subjects receiving intervention or placebo relative to absolute increases in 25-hydroxyvitamin D levels from day 0 to day 3.

RESULTS

55.2% of subjects randomized to high dose vitamin D₃ demonstrated an absolute increase in 25-hydroxyvitamin D ≥ 15 ng/ml from day 0 to day 3. With an absolute increase in 25-hydroxyvitamin D ≥ 15 ng/ml, multiple members of the sphingomyelin, plasmalogen, lysoplasmalogen and lysophospholipid metabolite classes had significantly positive Bonferroni corrected associations over time. Further, multiple representatives of the acylcarnitine and phosphatidylethanolamine metabolite classes had significantly negative Bonferroni corrected associations over time with an absolute increase in 25-hydroxyvitamin D ≥ 15 ng/ml. Changes in these highlighted metabolite classes were associated with decreased 28-day mortality.

CONCLUSIONS

Increases in 25-hydroxyvitamin D following vitamin D₃ intervention are associated with favorable changes in metabolites involved in endothelial protection, enhanced innate immunity and improved mitochondrial function.

Evaluating the impact of policies recommending PrEP to subpopulations of men and transgender women who have sex with men based on demographic and behavioral risk factors

INTRODUCTION

Developing guidelines to inform the use of antiretroviral pre-exposure prophylaxis (PrEP) for HIV prevention in resource-limited settings must necessarily be informed by considering the resources and infrastructure needed for PrEP delivery. We describe an approach that identifies subpopulations of cisgender men who have sex with men (MSM) and transgender women (TGW) to prioritize for the rollout of PrEP in resource-limited settings.

METHODS

We use data from the iPrEx study, a multi-national phase III study of PrEP for HIV prevention in MSM/TGW, to build statistical models that identify subpopulations at high risk of HIV acquisition without PrEP, and with high expected PrEP benefit. We then evaluate empirically the population impact of policies recommending PrEP to these subpopulations, and contrast these with existing policies.

RESULTS

A policy recommending PrEP to a high risk subpopulation of MSM/TGW reporting condomless receptive anal intercourse over the last 3 months (estimated 3.3% 1-year HIV incidence) yields an estimated 1.95% absolute reduction in 1-year HIV incidence at the population level, and 3.83% reduction over 2 years. Importantly, such a policy requires rolling PrEP out to just 59.7% of MSM/TGW in the iPrEx population. We find that this policy is identical to that which prioritizes MSM/TGW with high expected PrEP benefit. It is estimated to achieve nearly the same reduction in HIV incidence as the PrEP guideline put forth by the US Centers for Disease Control, which relies on the measurement of more behavioral risk factors and which would recommend PrEP to a larger subset of the MSM/TGW population (86% vs. 60%).

CONCLUSIONS

These findings may be used to focus future mathematical modelling studies of PrEP in resource-limited settings on prioritizing PrEP for high-risk subpopulations of MSM/TGW. The statistical approach we took could be employed to develop PrEP policies for other at-risk populations and resource-limited settings.

Preexposure Prophylaxis for the Prevention of HIV Infection: Evidence Report and Systematic Review for the US Preventive Services Task Force

IMPORTANCE

Effective prevention strategies for HIV infection are an important public health priority. Preexposure prophylaxis (PrEP) involves use of antiretroviral therapy (ART) daily or before and after sex to decrease risk of acquiring HIV infection.

OBJECTIVE

To synthesize the evidence on the benefits and harms of PrEP, instruments for predicting incident HIV infection, and PrEP adherence to inform the US Preventive Services Task Force.

DATA SOURCES

Ovid MEDLINE, the Cochrane Central Register of Controlled Trials, the Cochrane Database of Systematic Reviews, and EMBASE through June 2018, with surveillance through January 2019.

STUDY SELECTION

English-language placebo-controlled randomized clinical trials of oral PrEP with tenofovir disoproxil fumarate/emtricitabine or tenofovir disoproxil fumarate monotherapy; studies on the diagnostic accuracy of instruments for predicting incident HIV infection; and studies on PrEP adherence.

DATA EXTRACTION AND SYNTHESIS

Dual review of titles and abstracts, full-text articles, study quality, and data abstraction. Data were pooled using the Dersimonian and Laird random-effects model for effects of PrEP on HIV infection, mortality, and harms.

MAIN OUTCOMES AND MEASURES

HIV acquisition, mortality, and harms; adherence to PrEP; and diagnostic test accuracy and discrimination.

RESULTS

Fourteen RCTs (N = 18 837), 8 observational studies (N = 3884), and 7 studies of diagnostic accuracy (N = 32 279) were included. PrEP was associated with decreased risk of HIV infection vs placebo or no PrEP after 4 months to 4 years (11 trials; relative risk [RR], 0.46 [95% CI, 0.33-0.66]; I2 = 67%; absolute risk reduction [ARD], -2.0% [95% CI, -2.8% to -1.2%]). Greater adherence was associated with greater efficacy (RR with adherence ≥70%, 0.27 [95% CI, 0.19-0.39]; I2 = 0%) in 6 trials. PrEP was associated with an increased risk of renal adverse events (12 trials; RR, 1.43 [95% CI, 1.18-1.75]; I2 = 0%; ARD, 0.56% [95% CI, 0.09%-1.04%]) and gastrointestinal adverse events (12 trials; RR, 1.63 [95% CI, 1.26-2.11]; I2 = 43%; ARD, 1.95% [95% CI, 0.48%-3.43%]); most adverse events were mild and reversible. Instruments for predicting incident HIV infection had moderate discrimination (area under the receiver operating characteristic curve, 0.49-0.72) and require further validation. Adherence to PrEP in the United States in men who have sex with men varied widely (22%-90%).

CONCLUSIONS AND RELEVANCE

In adults at increased risk of HIV infection, PrEP with oral tenofovir disoproxil fumarate monotherapy or tenofovir disoproxil fumarate/emtricitabine was associated with decreased risk of acquiring HIV infection compared with placebo or no PrEP, although effectiveness decreased with suboptimal adherence.

Effects of a computerized psychological inoculation intervention on condom use tendencies in sub Saharan and Caucasian students: two feasibility trials

Objective: An effective method for preventing the Human Immunodeficiency Virus (HIV) is condom use. Yet, research shows limited effects of education on increasing condom use. This research examined the effects of psychological inoculation (PI) versus education on condom use -barriers and -tendencies, using a fully automatized online system. Design: Two randomized controlled trials. In Study 1, 59 Sub-Saharan students were included while Study 2 20 European students were included. In both studies, participants were randomly assigned to PI or control conditions. In Study 2, we additionally matched pairs on gender and condom barriers. In the PI, participants received challenging sentences they had to refute. Main outcome measures: An indirect condom use test (I-CUTE) and a condom use barriers questionnaire, assessed at baseline and a month later. Results: In Study 1, a significant increase in I-CUTE scores and no change in barriers was found in the PI condition. Controls did not change on either outcome. In Study 2, two sub-scales of condom barriers (concerning partner and satisfaction) were significantly decreased in the PI group, while in controls, barriers significantly increased over time. In both groups, I-CUTE scores tended to increase. Conclusions: These results replicate previous studies and extend them to a fully automatized system without counselors.

Taking stock of the present and looking ahead: envisioning challenges in the design of future HIV prevention efficacy trials

Despite the recent success of antiretrovirals for HIV prevention, additional, more effective, or more acceptable biomedical interventions will ultimately be needed to end the HIV epidemic. Designing clinical trials to evaluate the efficacy of new products that reduce HIV infection risk is challenging because of the existence of highly effective interventions to prevent HIV. However, the implementation of these interventions is uneven, and the fact that multiple HIV prevention efficacy trials are currently evaluating new products means the field confronts uncertainty in the emerging standard of prevention. In this Viewpoint, we take stock of the current state of HIV prevention, and subsequently discuss the key challenges in designing future trials to evaluate the next generation of HIV prevention products. We also highlight gaps in the knowledge base that need to be addressed to advance the design of research. Future trials are tenable, even in the context of existing and effective interventions, and should involve careful statistical approaches and multidisciplinary collaborative design.

Antiretroviral Therapy and Mortality in Rural South Africa: A Comparison of Causal Modeling Approaches

Estimation of causal effects from observational data is a primary goal of epidemiology. The use of multiple methods with different assumptions relating to exchangeability improves causal inference by demonstrating robustness across assumptions. We estimated the effect of antiretroviral therapy (ART) on mortality in rural KwaZulu-Natal, South Africa, from 2007 to 2011, using 2 methods with substantially different assumptions: the regression discontinuity design (RDD) and inverse-probability–weighted (IPW) marginal structural models (MSMs). The RDD analysis took advantage of a CD4-cell-count–based threshold for ART initiation (200 cells/μL). The 2 methods yielded consistent but nonidentical results for the effect of immediate initiation of ART (RDD intention-to-treat hazard ratio (HR) = 0.66, 95% confidence interval (CI): 0.35, 1.26; RDD complier average causal effect HR = 0.56, 95% CI: 0.41, 0.77; IPW MSM HR = 0.49, 95% CI: 0.42, 0.58). Although RDD and IPW MSM estimates have distinct identifying assumptions, strengths, and limitations in terms of internal and external validity, results in this application were similar. The differences in modeling approaches and the external validity of each method may explain the minor differences in effect estimates. The overall consistency of the results lends support for causal inference about the effect of ART on mortality from these data.

Weighing the Evidence of Efficacy of Oral PrEP for HIV Prevention in Women in Southern Africa

As oral tenofovir-based regimens for preexposure prophylaxis (PrEP) are adopted as standard of care for HIV prevention, their utilization in clinical trials among women in southern Africa will require an accurate estimate of oral PrEP efficacy in this population. This information is critical for women in choosing this prevention strategy, and in public health policy making. Estimates of the efficacy of oral PrEP regimens containing tenofovir have varied widely across trials that enrolled women, with some studies reporting high efficacy and others reporting no efficacy. Although poor adherence is strongly associated with lack of efficacy, other factors, such as mode of transmission (sexual vs. parenteral), predominant HIV subtype (C vs. non-C), intensity of exposure, and percentage of stable serodiscordant couples, may also contribute to the variation in efficacy estimates. In this article, we evaluate the evidence for PrEP efficacy in women and propose potential explanations for the observed differences in efficacy among studies. Our review emphasizes the need to continue to refine estimates of efficacy and effectiveness of tenofovir-based oral PrEP so as to best develop the next generation of HIV prevention tools, and to inform public policies directed toward HIV prevention.

Modeling HIV vaccine trials of the future

PURPOSE OF REVIEW

Models of implementation of known-effective interventions for HIV prevention indicate that an efficacious vaccine to prevent HIV infection would be critical for controlling the HIV pandemic. Key issues in the design of future HIV vaccine trials are: first, how to develop reliable immunological correlates of vaccine efficacy, second, how to down-select candidate vaccine regimens into efficacy trials, and third, how to learn about vaccine efficacy in the context of the evolving HIV prevention landscape.

RECENT FINDINGS

Whereas in the past phase-I/-II HIV vaccine trials have addressed the first and second points using a small set of immunological assays and readouts, recently they have used a battery of assays with highly multivariate readouts. In addition, systems vaccinology studies of other pathogens measuring PBMC transcriptomics and other immunological features pre- and postfirst vaccination are demonstrating value, for example, providing discoveries that preimmunization and early postimmunization cell population markers can predict the influenza-specific antibody titer that is a correlate of vaccine protection. The HIV prevention landscape continues to evolve, and the design and analysis of vaccine trials is evolving alongside, to accommodate increasingly dynamic and regional standards of HIV prevention.

SUMMARY

Development of interpretable and robust functional assays, in addition to the associated bioinformatics and statistical analytic tools, is needed to improve the assessment of correlates of protection in efficacy trials and the down-selection of candidate vaccine regimens into efficacy trials. Moreover, high-priority trials should integrate systems vaccinology, including the analysis of prevaccination and early postvaccination markers.

Implementation and Operational Research: Evolution of Couples' Voluntary Counseling and Testing for HIV in Rwanda: From Research to Public Health Practice

BACKGROUND

Couples' voluntary HIV counseling and testing (CVCT) is a WHO-recommended intervention for prevention of heterosexual HIV transmission which very few African couples have received. We report the successful nationwide implementation of CVCT in Rwanda.

METHODS

From 1988 to 1994 in Rwanda, pregnant and postpartum women were tested for HIV and requested testing for their husbands. Partner testing was associated with more condom use and lower HIV and sexually transmitted infection rates, particularly among HIV-discordant couples. After the 1994 genocide, the research team continued to refine CVCT procedures in Zambia. These were reintroduced to Rwanda in 2001 and continually tested and improved. In 2003, the Government of Rwanda (GoR) established targets for partner testing among pregnant women, with the proportion rising from 16% in 2003 to 84% in 2008 as the prevention of mother-to-child transmission program expanded to >400 clinics. In 2009, the GoR adopted joint posttest counseling procedures, and in 2010 a quarterly follow-up program for discordant couples was established in government clinics with training and technical assistance. An estimated 80%-90% of Rwandan couples have now been jointly counseled and tested resulting in prevention of >70% of new HIV infections.

CONCLUSIONS

Rwanda is the first African country to have established CVCT as standard of care in antenatal care. More than 20 countries have sent providers to Rwanda for CVCT training. To duplicate Rwanda's success, training and technical assistance must be part of a coordinated effort to set national targets, timelines, indicators, and budgets. Governments, bilateral, and multilateral funding agencies must jointly prioritize CVCT for prevention of new HIV infections.

Invited commentary: every good randomization deserves observation

Preexposure prophylaxis (PrEP) is a promising approach to prevention of human immunodeficiency virus (HIV) transmission, in which an HIV-negative individual takes a single daily dose of an antiretroviral drug so that, if exposed to HIV, an active antiretroviral drug is already present in his or her system. In this issue of the Journal, Murnane et al. (Am J Epidemiol. 2015;182(10):848-856) use data from the Partners PrEP Study (Kenya and Uganda, 2008-2011) to estimate the efficacy of PrEP under perfect adherence. We discuss Murnane et al.'s work and then examine the larger issues of generalizability or transportability of findings from a randomized trial to a new setting when adherence to an intervention determines its effectiveness. We discuss sufficient conditions for generalizability and use causal directed acyclic graphs to show how these assumptions might play out when trials are used to make inferences about the effect of PrEP in current and future real-world target populations.