Cabotegravir Maintains Protective Efficacy in the Setting of Bacterial STIs: A Secondary Analysis of HPTN 083

Background: Sexually transmitted infections (STIs) have been shown to facilitate HIV transmission and acquisition. HPTN 083, a global clinical trial, demonstrated superiority of long-acting cabotegravir (CAB-LA) versus daily oral tenofovir disoproxil fumarate/emtricitabine (TDF/FTC) for HIV prevention among transgender women and cisgender men who have sex with men. This analysis assessed whether CAB-LA maintained protective efficacy when bacterial STIs (syphilis, rectal/urethral gonorrhea and chlamydia) were present.

Methods: STI events per 100 person-years (PY) were calculated, including by subgroups (age, race/ethnicity, gender, education, treatment arm, drug use, alcohol use, region/country, condom usage, partner number, marital status, baseline STI). Association between baseline factors and STI incidence was modeled using Poisson regression. Cox proportional hazards modeling with STI status as a time-varying covariate was used to evaluate potential interactions between STI status and the relative efficacy of CAB-LA vs. TDF/FTC.

Findings: Among 3,859 participants, overall STI incidence rate was 50.7 infections/100PY. STIs were diagnosed in 1,562 (40.5%) participants; 79% of STIs occurred in 25% of the participants. STI incidence was not different by PrEP arm. In the final multivariable model, age, region, race, education level, marital status, and baseline STI were associated with incident STI (p<0.05). HIV incidence was lower with CAB-LA vs. TDF/FTC with or without STIs (hazard ratios 0.37 and 0.31, respectively), with no significant interaction between STIs and the HR for HIV incidence (p = 0.75).

Conclusion: In a large PrEP trial with high STI incidence, CAB-LA maintained robust protective efficacy relative to TDF/FTC in the setting of bacterial STIs.