Can a pill and a vaccine stop STIs in High-Risk men?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Mens who have sex with mens (MSM) enrolled in the ANRS PREVENIR study. * At least 6-month experience with PrEP (within the ANRS PREVENIR study or before starting the ANRS PREVENIR study). * No clinical manifestation of primary HIV infection and no symptom of bacterial STI (chlamydia, gonorrhea, M. genitalium or syphilis). * History of documented bacterial STI with at least one episode in the last 12 months. * Participants who agree to sign the information and consent form specific to this study. * Valid health insurance (State medical aid (AME) is not health insurance). Exclusion Criteria: * Syphilis diagnosed prior to inclusion without serologic evidence of cure (cure is defined as decreased by at least 4-fold of the non-treponemal antibody titer \[Venereal Disease Research Laboratory (VDRL), Rapid Plasma Reagin (RPR)\] relative to the titer at initiation of treatment of syphilis). * HIV infection. * Previous vaccination with Bexsero® or any other meningococcal B vaccine. * Vaccination during the 4 weeks (28 days) preceding the first vaccination of the study. * Previous vaccination with an experimental vaccine in the previous 5 years. * Systemic treatment with retinoids : isotretinoin (Acnetrait®, Procuta®, Curacné®, Contracné®, …). * Treatment with enzyme-inducing anticonvulsants (carbamazepine, phenobarbital, phenytoin, ….). * Participant who has received immunoglobulins, a transfusion of blood or blood derivatives in the last 3 months. * Known or suspected congenital or acquired immunodeficiency; immunosuppressive treatment in the last 6 months, such as cancer chemotherapy or radiotherapy; long-term systemic corticosteroid therapy (prednisone or equivalent for more than 2 consecutive weeks in the last 3 months) * Known allergy to antibiotics of the tetracycline family. * Known allergy to any component of the Bexsero® vaccine. * Known allergy to any component of the doxycycline pill. * Known allergy to latex (contained in the vaccine cap). * Thrombocytopenia or any other known coagulation disorder, which would be a contraindication to an intramuscular injection of Bexsero® vaccine. * Documented oesophageal lesion * Acute respiratory infection or severe acute febrile illness or systemic reaction that may present a significant risk if vaccinated in the month prior to inclusion. * Any condition (clinical) that, in the investigator's opinion, would contraindicate intramuscular vaccination and blood sampling. * Oral Anticoagulant treatment. * Continuous treatment with doxycycline at inclusion. * Vitamin A treatment in case of intake of 10 000 international unit or more. * Participation in another research including an exclusion period still in progress at the time of inclusion. * Under guardianship or curator, or deprived of liberty by a judicial or administrative decision.