Prevention was in the spotlight at the 30th edition of the Conference on Retroviruses and Opportunistic Infections (held on February 19-22 in Seattle, US) and particularly the prevention of sexually transmitted infections (STIs). Two effective strategies were presented. For bacterial STIs, a French study has confirmed the efficacy of a preventive dose of a well-known antibiotic, doxycycline, taken one to three days after unprotected sexual intercourse. This antibiotic is traditionally recommended for the treatment of infections in the urethra, cervix, fallopian tubes or anus. It is also recommended in the treatment of syphilis, Lyme disease, some skin diseases (rosacea and acne), dental infections and diarrhea of bacterial origin, as well as in the prevention of malaria.
The notion of postexposure prevention with doxycycline emerged in late 2017 during the Ipergay trial, conducted by the French National Agency for Research on AIDS and Viral Hepatitis (ANRS). Taken within 24 to 72 hours after sex, this antibiotic reduces the risk of chlamydia and syphilis infection by about 70%.
In recent years, various epidemiological studies have also reported that people vaccinated against meningococcus B (with GSK’s Bexsero vaccine) could see a reduction in the risk of gonococcal infection of about 30%. “There are common antigens between meningococcus B and gonococcus,” said Jean-Michel Molina, head of the department of infectious and tropical diseases at Saint-Louis Hospital and Lariboisière Hospital (Paris-Cité University), hence a possible cross-protection against this STI provided by the meningococcal vaccine.
No severe side effects
The DoxyVAC study, coordinated by Molina, was promoted and funded by the ANRS. Between January 2021 and July 2022, researchers recruited 502 male volunteers (average age 39) who had sex with men (with an average of 10 sexual partners in the past three months) and lived in the Paris area. All were on PrEP (an HIV preventive treatment) and had a history of STIs in the previous year. They were randomly assigned to four groups, according to the rules of randomized trials. The first received postexposure prevention with doxycycline (within 24 to 72 hours after unprotected sex), the second received a meningococcal B vaccination, the third received a combination of these two interventions and the last had no intervention.
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On doxycycline, the risk of chlamydia or syphilis infection was reduced by 84% and the risk of gonococcal infection (gonorrhea) by 51%, over a median of nine months. In the group that received two doses of meningococcal B vaccine, the risk of gonorrhea was reduced by 51%. “This is the first time a vaccine has been shown in a randomized trial to reduce the risk of a bacterial STI,” said Professor Molina. There were no severe adverse events associated with either intervention.
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