Infectious Disease · Medical Literature
Efficacy of the 4CMenB vaccine against gonorrhea among men who have sex with men in Hong Kong: A double-blind randomized placebo-controlled trial.
Abstract
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. 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. 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. 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.
Clinical relevance
Does the two-dose 4CMenB (four-component meningococcal group B) vaccine reduce the incidence of gonorrhea in men who have sex with men (MSM) aged 18–50 years compared with placebo over one year of follow-up? __SNAPSHOT__ {"studyDesign":"Prospective, randomized, double-blind, placebo-controlled trial (NCT05766904)","setting":"Hong Kong; single country; clinical trial setting, 2023–2024","sampleSize":"n=152 (vaccine arm: 76, control arm: 76); 1:1 allocation using permuted blocks of four","population":"MSM aged 18–50 years; specific inclusion/exclusion criteria beyond age and sexual orientation not reported in abstract","intervention":"Two intramuscular injections of 4CMenB (Bexsero) at least one month apart","comparator":"Placebo (two injections at matched intervals)","primaryOutcome":"Incidence of first gonorrhea episode within the first year of follow-up","followUp":"3-monthly visits over 2 years (primary outcome assessed at 1 year)","fundingSource":"Not reported in abstract"}
Key findings
The primary outcome — incidence of first gonorrhea episode in year one — did not differ significantly between arms. The control arm incidence rate was 0.78 (95% CI 0.64–0.95) and the vaccine arm rate was 0.86 (95% CI 0.77–0.96); the hazard ratio was 0.76 (95% CI 0.31–1.87), crossing unity and thus demonstrating no statistically significant protective effect. The wide confidence interval (spanning from a possible 69% relative risk reduction to an 87% relative risk increase) reflects the study's limited statistical power given the small sample size of 152 participants, and no meaningful efficacy conclusion can be drawn from the point estimate alone. NNT is not calculable given the absence of efficacy. Participants in the vaccine arm were more likely to experience adverse effects (specific rates not reported in abstract). A secondary behavioral finding of concern: after unblinding, vaccinated participants reported reduced worry about acquiring gonorrhea (adjusted OR 2.10, 95% CI 1.22–3.59) and lower condom use rates compared with the control arm, raising the possibility of risk compensation in a real-world implementation scenario.
Practice implications
This trial did not demonstrate efficacy of 4CMenB against gonorrhea in MSM, consistent with findings from larger contemporaneous RCTs (GoGoVax, NEJM 2026; MenGO, npj Vaccines 2026; DOXYVAC). However, this study is substantially underpowered (n=152) and cannot independently confirm or refute vaccine efficacy; the 95% CI for the hazard ratio is too wide to exclude either a clinically meaningful benefit or harm. The GoGoVax trial (n=587 in per-protocol analysis) reported a vaccine efficacy of −0.5% (95% CI −26.2 to 19.9), providing substantially stronger evidence of no effect in a comparable high-risk MSM population. The behavioral finding of post-unblinding risk compensation — reduced condom use among vaccinated participants — is a clinically important safety signal independent of immunological efficacy: even if a future vaccine proved effective, risk compensation could attenuate or negate population-level benefit. Patients inadequately represented include women, transgender individuals, MSM at lower baseline gonorrhea risk, heterosexual men, and populations outside Hong Kong. Findings apply most cautiously to high-risk MSM in a concentrated urban epidemic setting. Only the abstract was available for review; granular data on adverse events, microbiological endpoints, protocol-defined per-protocol vs. intention-to-treat analyses, and behavioral outcome measurement instruments are not reportable. __LIMITATIONS__ Critically underpowered: n=152 yields a hazard ratio 95% CI of 0.31–1.87, making any efficacy conclusion statistically unreliable; the trial was likely not designed as a definitive efficacy study.,Single-center, single-country (Hong Kong) design limits generalizability to other geographic, epidemiological, and genomic gonococcal strain contexts.,Primary outcome (year-one incidence) uses only half the stated 2-year follow-up period; year-two data not reported in abstract.,Behavioral outcomes (condom use, worry) were assessed post-unblinding, introducing unblinding bias and precluding blinded behavioral assessment.,Specific adverse event rates, severity grading, and per-protocol vs. intention-to-treat analyses are not reported in the abstract.,Gonorrhea diagnosis methodology (NAAT, culture, anatomical sites screened) not reported, limiting assessment of outcome ascertainment quality.,Funding source not reported; cannot assess industry influence or independence.,The observed HR of 0.76 is directionally consistent with prior observational data suggesting modest cross-protection, but given the CI width, this cannot be interpreted as evidence of efficacy.,Only abstract available; full-text review is required before incorporating these findings into clinical decision-making. __BOTTOM_LINE_CATEGORY__ confirmatory __BOTTOM_LINE__ This small Hong Kong RCT (n=152) found no statistically significant efficacy of 4CMenB against gonorrhea in MSM (HR 0.76, 95% CI 0.31–1.87), though it was substantially underpowered to serve as a definitive efficacy trial. Its finding is directionally concordant with larger, adequately powered RCTs (GoGoVax, MenGO, DOXYVAC) that collectively provide compelling evidence against using 4CMenB for gonorrhea prevention in high-risk MSM. The observed post-unblinding risk compensation — lower condom use in vaccinated participants — constitutes an important secondary signal that warrants consideration in any future vaccine rollout strategy.