Evaluating adherence in an active-controlled HIV pre-exposure prophylaxis trial (PrEPVacc) to inform the estimation of HIV incidence in a counterfactual placebo arm

Sheila Kansiime ORCID logo ; Christian Holm Hansen ; Henry Bern ; Julie Fox ; David Dunn ; Eugene Ruzagira ORCID logo ; Richard Hayes ORCID logo ; Sheena Mc Cormack ; Glenda Gray ; Nishanta Singh ; +98 more... Zakir Gaffoor ; Neetha Morar ; Thandiwe Sithole ; Kubashni Woeber ; Samantha Siva ; Eldi-nah Hwengwere ; Rujeko Samanthia Chidawanyika ; Nteboheleng Mahapa ; Phindile Khanyile ; Janet Seeley ; Lucas Maganga ; Wiston William ; Emmanuel Kapesa ; Elizabeth Danstan ; Doreen Pamba ; Marco Missanga Amani Kway ; Abisai Kisinda ; Lilian Njovu ; Lwitiho Sudi ; Revocatus Kunambi ; Jane Ambindwile ; Said Aboud ; Patricia Munseri ; Eligius Lyamuya ; Frank Msafiri ; Agricola Joachim ; Edith Tarimo ; Diana Faini Tumaini Nagu ; Deus Buma ; Muhammad Bakari ; Pontiano Kaleebu ; Freddie Mukasa Kibengo ; Ayoub Kakande ; Jennifer Serwanga ; Janet Seeley ; Rachael Kawuma ; Sylvia Kusemererwa ; Anita Kabarambi ; Martin Onyango ; Jonathan Kitonsa ; Sylvia Masawi ; Vincent Basajja ; Tobias Vudriko ; Peter Hughes ; Florence Nambaziira ; Shamim Nabukenya ; Gertrude Mutonyi ; Rita Nakiboneka ; Susan Mugaba ; Sarah Nakamanya ; Denis Kibuuka ; Bernadette Kalanzi ; Ilesh Jani ; Edna Viegas ; Isabel Remane ; Odete Bule ; Edna Nhacule ; Patricia Ramgi ; Raquel Chissumba ; Eduardo Namalango ; Yolanda Manganhe ; Carmelia Massingue ; Igor Capitine ; Jorge Ribeiro ; Jonathan Weber ; Cherry Kingsley ; Thomas E Miller ; Sarah Joseph ; Claire Wenden ; Giuseppe Pantaleo ; Song Ding ; James S Rooney ; Alex Kintu ; Iera Monasterio ; Lisette Bassi ; Arne Kroidl ; Merlin Robb ; Charlotta Nilsson ; Carter Lee ; Vineeta Gulati ; Gustavo Doncel ; Jessica Maitz ; Annie Thurman ; Sheena McCormack ; Simona Salomone ; Angela Crook ; David Dunn ; Henry Bern ; Aminata Sy ; Liz Brod-nicki ; Julie Fox ; Kundai Chinyenze ; Jacqueline Musau ; Mabela Matsoso ; Mary Amondi ; Ansuya Naidoo ; Paramesh Chetty ; Anne Gumbe ; (2025) Evaluating adherence in an active-controlled HIV pre-exposure prophylaxis trial (PrEPVacc) to inform the estimation of HIV incidence in a counterfactual placebo arm. HIV Research & Clinical Practice, 26 (1). 2513684-. ISSN 2578-7489 DOI: 10.1080/25787489.2025.2513684
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<h4>Background</h4>Inferring the counterfactual placebo HIV incidence using the estimated effectiveness of Emtricitabine/Tenofovir (TDF/FTC) in active-controlled pre-exposure prophylaxis (PrEP) trials has been suggested. However, it has not yet been widely applied. In this article, we evaluate adherence to TDF/FTC in the PrEPVacc trial (NCT04066881) and consider how such adherence data could be used to estimate the effectiveness of TDF/FTC and subsequently, HIV incidence in a counterfactual placebo arm in a predominantly female population.<h4>Methods</h4>From December 2020 to March 2023 participants were recruited into the trial which included a comparison of Emtricitabine/Tenofovir Alafenamide (TAF/FTC) to TDF/FTC as PrEP over 26 weeks of follow-up, in Uganda, Tanzania, and South Africa. PrEP adherence was assessed in various ways.<h4>Results</h4>Of 697 participants dispensed TDF/FTC, 87% were female, 54% were ≥ 25 years, and 59% were sex workers. In a random sample (41%) assessed at visit 6 (week 8), 76% had detectable TFV-DP levels, with 22% reaching levels consistent with ≥2 pills/week. Males, Verulam and Mbeya participants, those ≥ 25 years, not single, subsistence fisheries workers, and those who had any STI at baseline were more likely to have higher adherence. Of those assessed at visit 6, 29% were identified as white coat dosing. Estimated (crude) HIV incidence risk reduction ranged from 10% to 65%.<h4>Conclusions</h4>TDF/FTC adherence in the PrEPVacc trial was low, with considerable levels of white coat dosing. Inferring the counterfactual placebo HIV incidence using the estimated effectiveness of TDF/FTC is a promising approach, however, the approach requires further elaboration and evaluation.


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