World's Largest RCT Finds Meningococcal B Vaccine Does Not Prevent Gonorrhoea

The meningococcal B vaccine known as 4CMenB does not prevent gonorrhoea. That is the conclusion of the world's largest randomized controlled trial testing the question - and it directly contradicts the observational evidence that has led several countries to offer the vaccine to gay and bisexual men considered at high risk of the sexually transmitted infection.

The GoGoVax trial, conducted by Griffith University's Institute for Biomedicine and Glycomics and the Kirby Institute at UNSW Sydney, enrolled 587 gay and bisexual men in a double-blind, randomized, placebo-controlled design. Participants received either 4CMenB or a saline placebo. The gonorrhoea incidence rate was virtually identical in both groups - approximately 48 percent per year. Professor Kate Seib, who led the trial, presented the results at the Conference on Retroviruses and Opportunistic Infections in Denver on February 25, 2026.

Why the observational studies got it wrong

The finding inverts a body of evidence that seemed, until now, reasonably coherent. Multiple observational studies - particularly case-control analyses - had suggested that individuals who received 4CMenB showed lower gonorrhoea rates compared to controls. Based on that evidence, health authorities in several countries began recommending the vaccine for high-risk individuals.

The problem is confounding. Case-control studies comparing vaccination histories of people with gonorrhoea against those with chlamydia may be measuring differences in health-seeking behavior, access to care, or other unmeasured variables rather than a genuine protective effect of the vaccine. Randomization eliminates this problem by distributing all confounding factors equally between groups. In GoGoVax, the researchers confirmed that good-quality randomization was achieved - balanced confounding factors across both arms - which is why the identical incidence rates carry substantial evidential weight.

The specific population enrolled

GoGoVax enrolled gay and bisexual men with a recent history of gonorrhoea or syphilis - a population chosen because their higher baseline risk made gonorrhoea acquisition over the study period more likely, allowing the trial to detect a protective effect if one existed. The researchers note one caveat: this history of prior infection may have altered immune dynamics in ways that reduce susceptibility to any potential vaccine effect. The results should not be generalized to all populations without this limitation in mind.

Implications for prevention

Gonorrhoea remains a significant public health challenge. Antibiotic-resistant strains are spreading, and the pipeline for new antibiotics effective against Neisseria gonorrhoeae is limited. An effective vaccine would substantially change prevention options. GoGoVax makes clear that 4CMenB is not that vaccine - at least not for gay and bisexual men at high risk. Men who received 4CMenB retain protection against some meningococcal strains - the vaccine's approved indication - but will need to rely on condom use and regular testing for STI prevention.

The trial results, combined with a smaller open-label trial called DOXYVAC that also showed no gonorrhoea protection, constitute the most direct evidence available on this question. Observational studies suggesting the vaccine worked will need to be reinterpreted in light of the confounding factors that a properly conducted RCT eliminates.