Counterfactual estimation of efficacy against placebo for novel PrEP agents using external trial data: example of injectable cabotegravir and oral PrEP in women

Perceptions of the attributes of new long-acting HIV pre-exposure prophylaxis formulations compared with a daily, oral dose among South African young women: a qualitative study

Oral PrEP is highly effective against the acquisition of HIV but is underutilised by young women. New options, like the monthly dapivirine vaginal ring (DVR) and injectable long-acting cabotegravir (CAB-LA), are emerging. However, little is known about young women's perceptions of these alternatives. This qualitative study explored perceptions of the attributes of PrEP technologies in South Africa. Young women accessing sexual health services were purposively selected to participate in 22 in-depth interviews, five focus group discussions and two workshops using the nominal group technique, between August 2022 and March 2023. A thematic approach guided by the diffusion of innovation attributes, including relative advantage, compatibility with the student's lives, complexity of the technology, and trialability, was used for data analysis. The DVR was the least preferred because of lower efficacy, the perceived complexity of inserting it in the vagina and some safety concerns. Oral PrEP, which some had tried and discontinued, was least compatible with students' busy schedules. Integrating PrEP and contraceptives with similar return visit patterns could enhance service delivery. Intensive demand creation campaigns will be needed to increase PrEP utilisation and dispel myths about the vaginal ring.

The potential benefits of long-acting injectable cabotegravir in pregnant and breastfeeding women and their infants

BACKGROUND

Pregnant and breastfeeding women (PBW) in sub-Saharan Africa have high HIV incidence rates and associated risk of vertical transmission to their infants. Oral preexposure prophylaxis (PrEP) and injectable PrEP (long-acting cabotegravir, or CAB-LA) can potentially reduce this HIV transmission, but population-level impacts are uncertain.

METHODS

We extended a previously developed model of HIV and PrEP in South Africa to allow for variable PrEP duration and preference in PBW. We considered three potential scenarios for PrEP provision to PBW: oral PrEP only, CAB-LA only, and allowing oral/CAB-LA choice, with uptake and retention assumptions informed by South African data, each compared with a 'base' scenario without PrEP for PBW.

RESULTS

Without PrEP for PBW, the model estimates 1.31 million new infections will occur between 2025 and 2035 in South African adults and children, including 100 000 in PBW, 16 800 in infants at/before birth, and 35 200 in children through breastmilk. In the oral PrEP-only scenario, these numbers would reduce by 1.2% (95% CI: 0.7-1.7%), 8.6% (4.8-12.9%), 4.0% (2.1-5.8%), and 5.3% (3.0-8.2%) respectively. In the CAB-LA-only scenario, the corresponding reductions would be 6.1% (2.9-9.6%), 41.2% (19.8-65.0%), 12.6% (6.0-19.4%), and 29.5% (13.9-46.8%), respectively, and in the oral/CAB-LA choice scenario, similar reductions would be achieved [5.6% (3.4-8.0%), 39% (23.4-55.9%), 12.4% (7.4-16.8%) and 27.6% (16.5-39.9%) respectively].

CONCLUSION

CAB-LA has the potential to be substantially more effective than oral PrEP in preventing HIV acquisition in PBW and vertical transmission, and can also modestly reduce HIV incidence at a population level.

Fusing trial data for treatment comparisons: Single vs multi-span bridging

While randomized controlled trials (RCTs) are critical for establishing the efficacy of new therapies, there are limitations regarding what comparisons can be made directly from trial data. RCTs are limited to a small number of comparator arms and often compare a new therapeutic to a standard of care which has already proven efficacious. It is sometimes of interest to estimate the efficacy of the new therapy relative to a treatment that was not evaluated in the same trial, such as a placebo or an alternative therapy that was evaluated in a different trial. Such dual-study comparisons are challenging because of potential differences between trial populations that can affect the outcome. In this article, two bridging estimators are considered that allow for comparisons of treatments evaluated in different trials, accounting for measured differences in trial populations. A "multi-span" estimator leverages a shared arm between two trials, while a "single-span" estimator does not require a shared arm. A diagnostic statistic that compares the outcome in the standardized shared arms is provided. The two estimators are compared in simulations, where both estimators demonstrate minimal empirical bias and nominal confidence interval coverage when the identification assumptions are met. The estimators are applied to data from the AIDS Clinical Trials Group 320 and 388 to compare the efficacy of two-drug vs four-drug antiretroviral therapy on CD4 cell counts among persons with advanced HIV. The single-span approach requires weaker identification assumptions and was more efficient in simulations and the application.

Post-exposure prophylaxis to prevent HIV: new drugs, new approaches, and more questions

Post-exposure prophylaxis (PEP) to prevent HIV acquisition has been recommended for over three decades, but remains underutilised. Over the past decade, clinical trials have established the safety and tolerability of newer PEP regimens, particularly those containing integrase strand transfer inhibitors (INSTIs) combined with a tenofovir and lamivudine or emtricitabine backbone. Several of these regimens were better tolerated than historical controls. Studies in macaques found that shorter courses of PEP with INSTIs were effective, particularly if dosing occurred close to the time of retroviral exposure. Despite the increase in well tolerated options, PEP seems to be underused globally and links to other prevention services are suboptimal. Interventions to increase provider and community awareness of PEP are needed.