Efficacy of the 4CMenB vaccine against gonorrhea among men who have sex with men in Hong Kong: A double-blind randomized placebo-controlled trial

INTRODUCTION: The emergence of antimicrobial-resistant gonorrhea among men who have sex with men (MSM) demands new prevention strategies. This study aimed to assess the efficacy of the four-component meningococcal group B (4CMenB) vaccine against gonorrhea among MSM. METHODS: A prospective, randomized, double-blind, placebo-controlled trial (NCT05766904) was conducted in Hong Kong in 2023-2024. In total, 152 MSM aged between 18 and 50 years were randomized to either the vaccination or control arm in a 1:1 ratio using permuted blocks of four. Participants received two injections at least 1 month apart and attended three-monthly follow-ups for 2 years. The primary outcome was the incidence of the first gonorrhea episode in the first year. RESULTS: Gonorrhea incidence in the two arms was comparable (control arm 0.78 (95% confidence interval [CI] 0.64-0.95); vaccine arm 0.86 (95% CI 0.77-0.96); hazard ratio 0.76, 95% CI 0.31-1.87). Participants in the vaccine arm were more likely to experience adverse effects, be less worried about acquiring gonorrhea (adjusted odds ratio 2.10, 95% CI 1.22-3.59), and have a lower condom use rate after unblinding. CONCLUSIONS: The results did not show efficacy of the 4CMenB vaccine against gonorrhea in MSM. Receipt of the vaccine may impact risk perception and behavioral practices, thus affecting vaccinees' exposure risk to sexually transmitted infections.