This is a randomized study with a factorial design for the 2 biomedical interventions (interventions 1 and 2).~Subjects will be randomized and assigned to two different interventions:~Intervention 1: PEP with doxycycline or no PEP. Subjects will be randomized 2/1 to receive doxycycline PEP or no PEP~Intervention 2: Meningococcal B vaccine (Bexsero®) or no vaccine Subjects will be randomized 1/1 to received 2 doses of Bexsero® vaccine (at the first visit and two months later) or no vaccine~Participants will be randomized in one of the following arms:~Arm 1: doxycycline and Bexsero® vaccine (240 participants)~Arm 2: doxycycline and no Bexsero® vaccine (240 participants)~Arm 3: no doxycycline and Bexsero® vaccine (120 participants)~Arm 4: no doxycycline and no Bexsero® vaccine (120 participants)~Randomization will be stratified by whether or not the participant enters in the ancillary study intestinal microbiota.
The study ANRS 174 Doxyvac is a clinical trial that will use Combined Prevention of Sexually Transmitted Infections (STIs) in Men Who Have Sex with Men and using oral TDF/FTC for HIV Pre-Exposure Prophylaxis (PrEP) and vaccination with Bexsero.