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Results from a major randomised control trial provide strong evidence that the meningococcal B vaccine is not effective at preventing gonorrhoea among gay and bisexual men.

Contrary to existing evidence from observational studies, the meningococcal B vaccine (4CMenB) has no effect on preventing the acquisition of gonorrhoea, according to the results of the world’s largest randomised control trial (RCT) into possible efficacy, conducted by ’s and the at 91ɫ��Ƭ Sydney.

The results were presented today by from Griffith University at the in Denver, Colorado.

Gonorrhoea is a considerable public health challenge, with particular concern around the rise in antibiotic-resistant strains. Gay and bisexual men were the focus of this study, as they are at particularly high risk of gonorrhoea.

The double-blind, randomised, placebo-controlled trial involved 587 gay and bisexual men who received either the meningococcal vaccine or a saline placebo.

“Across both arms, the gonorrhoea incidence was virtually the same – at around 48 per cent per year, indicating very clearly that the vaccine had no effect on preventing gonorrhoea,” said Prof. Seib, who led the trial.

“Our results support findings from the smaller DOXYVAC open-label trial that also showed no effect.

“Taken together, these two studies provide strong evidence that the 4CMenB meningococcal vaccine is not effective at preventing gonorrhoea in gay and bisexual men who are at high risk of contracting it.”

Other options are necessary to combat gonorrhoea

“An effective vaccine to reduce gonorrhoea would transform our approach to prevention, so it is incredibly disappointing that our research has proven that 4CMenB is not effective in gonorrhoea prevention in gay and bisexual men,” said from the Kirby Institute, who was also a lead on the study.

The meningococcal B vaccine was approved for use in Australia in 2013 and is a very safe and effective vaccine at preventing meningococcal disease.

“We want men who have received the 4CMenB vaccine in the hope of gonorrhoea prevention to know that the vaccine is very safe and they will have protection against some meningococcal strains. However, these men will need to explore other options for prevention of acquisition of gonorrhoea, such as condoms and regular testing. Services like sexual health clinics and community-based testing services are strong pillars of prevention,” Prof. Grulich said.

This RCT was conducted amongst gay and bisexual men who had a recent history of gonorrhoea or syphilis, and these groups were chosen as they were more likely to acquire gonorrhoea over the course of the study.

It is possible that the high rates of gonorrhoea history among this particular study population make them less susceptible to any potential protective effects of vaccination.

The results of this study cannot be generalised to other populations, however they represent an important finding for gay and bisexual men at high risk.

“Research like this is vital because it helps give our communities the clarity we need. Findings help us refine our approach in preventing the transmission of STIs. We thank everyone who participated in the study. Your contribution will help strengthen sexual health in our communities,” said Brent Mackie, Director of Policy, Strategy and Research at , who was a collaborator on the study.

Why do observational studies sometimes get it wrong?

The RCT called ‘’ was initiated by Griffith University and the Kirby Institute following several observational studies which suggested that the meningococcal B vaccine was associated with reduced gonorrhoea incidence. Based on these data, there are several countries where gay and bisexual men who are considered at high risk for gonorrhoea are being offered the vaccine. 

However, observational studies can be affected by what researchers call confounding factors.

For example, case-control studies look back in time to compare people with a disease to people without it, to learn about possible causes or ways to prevent the illness.

“Some case-control studies have compared the meningococcal B vaccination history of people who have gonorrhoea to the vaccination history of people who have chlamydia. In these studies, people who acquired gonorrhoea had lower 4CMenB vaccination rates than expected, suggesting that the vaccine may have prevented gonorrhoea. However, other confounding factors might explain the differences in vaccine history between the other two groups,” said Prof. Grulich.

RCTs are considered the gold standard in medical research because if conducted correctly, randomisation removes all possible confounding factors.

“In GoGoVax, our data demonstrate that good-quality randomisation was achieved, and people randomised to receive vaccine or placebo had balanced levels of confounding factors. A properly conducted RCT provides the strongest possible evidence of a cause-and-effect relationship,” said Prof Grulich. 

“While the finding is disappointing, we want to acknowledge the engagement of gay and bisexual men in this research, and their ongoing resilience. It's important we continue to work in partnership to investigate different options for gonorrhoea prevention.”