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OA02.05LB M. Malahleha (1); H. Janes (2); F. Laher (3); L.-G. Bekker (4); B. S. Prigmore (5); D. Grove (5); J.J. Kee (5); M. Allen (6); M. Andrasik (2); M. [...], Background: South Africa has the highest HIV incidence globally. HIV risk has been extensively studied in South African cisgender women; however, less is known about risk drivers in cisgender men and transgender women (TGW). We characterised HIV incidence, and sexual behaviours and clinical characteristics associated with HIV acquisition, amongst cisgender men and TGW in two South African HIV vaccine efficacy trials. Methods: We included data from heterosexual cisgender men (HCM), men who have sex with men (MSM) and TGW who participated in Uhambo (N = 1611 randomised to vaccine/placebo, 2016 to 2020) and Phambili (N = 219 randomised to placebo, 2007 to 2011; vaccinees excluded due to potential vaccine-increased risk). Cox proportional hazards models were used to associate baseline variables--self-reported last thirty-days (Uhambo) or six-months (Phambili) sexual behaviours and laboratory-confirmed STIs--with HIV acquisition. Results: Median age was 25 (IQR: 22 to 30). Most identified as heterosexual or reported no male partner (1636/1830 [89.40%]). More MSM and TGW versus HCM reported anal sex (90.21% vs. 5.01%), transactional sex (41.75% vs. 11.37%), [greater than or equal to]2 partners (82.99% vs. 65.28%), sex with alcohol/drugs (67.53% vs. 55.50%) or sex with an HIV-positive partner (71.65% vs. 44.74%). Overall HIV incidence was 1.32% annually (95% CI: 0.99 to 1.74) and higher in MSM and TGW (8.84%, 95% CI: 5.40 to 13.65) or those with an STI (2.99%, 95% CI: 1.63 to 5.01). Based on multiplicity-adjusted univariate analyses, anal sex (HR 6.34, 95% CI: 3.45 to 11.66), transactional sex (HR 3.42, 95% CI: 1.80 to 6.51), and MSM or homosexual identity (HR 15.62, 95% CI: 7.82 to 31.81) were significantly associated with HIV acquisition. In a multivariate model of published HIV risk factors, only MSM and homosexual identity (HR 12.90, 95% CI: 4.03 to 41.29; p < 0.001) was significantly associated with HIV acquisition. Conclusions: Identifying as MSM or homosexual is a strong predictor of HIV acquisition in South African men and TGW. While overall incidence in cisgender men and TGW is low relative to women, subpopulations of cis-gender men and TGW experience exceptionally high incidence.