Abstract Body


Increased rates of sexually transmitted infections (STI) are reported among men who have sex with men (MSM), in particular those using pre-exposure prophylaxis for HIV (PrEP). Interventions to reduce STI incidence are needed.


MSM on PrEP with a history of STI in the past year, were randomized in an open-label factorial design trial to receive doxycycline post-exposure prophylaxis (Doxy PEP: 200 mg within 72h of condomless sex) or no PEP (2:1); and 2 shots of meningococcal B vaccine (Bexsero°) or no vaccine (1:1). Participants were tested centrally at baseline, every 3 months and when symptomatic for N. gonorrhoeae (GC) and C. trachomatis (CT) by PCR in throat, anus and urine. Serologic tests for syphilis were performed every 3 months. A committee adjudicated STI blinded to study arms. The co-primary endpoints were: the incidence of first episode of CT or syphilis for Doxy PEP and the incidence of a first episode of GC, 1 month after the second injection, for the vaccine intervention, using an intent-to-treat analysis. We used Cox proportional hazard models to compare incidence between Doxy PEP and no PEP adjusted for vaccine intervention and vice versa. Following external evidence, a single interim analysis occurred in September 2022 at the request of the DSMB who recommended to stop the trial for efficacy. Results for data collected up to July 15, 2022 are presented.


Between January 19, 2021, and July 15, 2022, 546 MSM were randomized and 502 were analyzed. Median age: 39 years, median of 10 sexual partners in past 3 months. Median follow-up: 9 months. There was no interaction between the two prevention strategies for the primary endpoints. The incidence of a first episode of CT or syphilis was 5.6 and 35.4 per 100 PY in the Doxy PEP and no PEP arms, respectively (aHR: 0.16; 95%CI: 0.08-0.30). The incidence of a first episode of GC was 20.5 and 41.3 per 100 PY in the Doxy PEP and no PEP arms, respectively (aHR: 0.49; 95%CI: 0.32-0.76). The incidence of a first episode of GC was 9.8 and 19.7 per 100 PY in the meningococcal B vaccine and no vaccine arms, respectively (aHR: 0.49; 95%CI: 0.27-0.88). No drug-related SAE was reported.


Among MSM on HIV PrEP, doxycycline PEP significantly reduced the incidence of CT and syphilis and also had a significant impact on the incidence of GC. Meningococcal B vaccine also reduced the incidence of GC.