An Australian expert has called for greater funding for a gonorrhoea vaccine after a second trial shows no protective effect.
New research from Griffith University and the Kirby Institute suggests the meningococcal B vaccine does not prevent gonorrhoea among gay and bisexual men.
Five hundred and eighty-seven gay and bisexual men were recruited as part of the GoGoVax trial, a double-blind, randomised and placebo-controlled trial. Participants received either two doses of the meningococcal vaccine (4CMenB) or two doses of placebo (normal saline), with the doses given three months apart. The men were then followed for 24 months to compare whether the rates of gonorrhoea development were different.
But the results of the trial, presented at the recent Conference on Retroviruses and Opportunistic Infections in Denver, Colorado, showed the 4CMenB vaccine had no effect.
“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,” Professor Kate Seib, a molecular microbiologist from Griffith University and lead researcher on the trial, said in a statement. “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.”
Professor Seib explained that Neisseria gonorrhoeae, the bacteria that causes gonorrhoea, is extremely adept at adapting to and evading the human immune response. These characteristics could contribute to why certain individuals – especially those with previous repeated cases of gonorrhoea – are less likely to benefit from vaccination.
“[The bacteria] has a lot of different mechanisms to do this. Either the bacterium changes the way it looks to our immune system, or it does something that dampens the ability of our immune system to make a protective response,” she told The Medical Republic.
The reduction modifiable protein (Rmp), a protein found on the outer membrane of N. gonorrhoeae, is believed to play a key role in this process.
“In certain situations, antibodies to the Rmp have been shown to decrease the ability of other antibodies to kill the bacteria,” Professor Seib said.
“If you’ve had a past infection and a previous immune response or antibodies to the bacteria, these existing antibodies may dampen the ability of the vaccine-induced immune response to do what it’s meant to do.
“The other side of it is that when you’re constantly exposed to [certain bacteria], it’s a bigger burden to completely prevent infection. It’s not a particularly scientific view, but I always think that with covid vaccines [for example], it’s harder to expect the vaccine to prevent infection if someone nearby has coughed and sneezed on you repeatedly compared to a more sporadic exposure.”
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Professor Andrew Grulich, an expert on the transmission and prevention of HIV and other sexually transmitted infections from the Kirby Institute, was incredibly disappointed by the results, but emphasised that the vaccine was still safe and effective 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,” he told media.
“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.
“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.”
Professor Seib said there were several international trials testing the meningococcal vaccine in lower-risk populations, including women, that could publish results by the end of the year.
“Men and women are quite different anatomically, but also at a molecular level. There are different receptors on the cells in the female genital tract compared to the cells in males, which means there are different mechanisms for infection between men and women,” she told TMR.
“[But] we do need to invest in additional research for a gonorrhoea vaccine, because even from the outset [of this line of work], observational studies predicted that only 30-40% of people would be protected. Which is a great start, but the more we understand [gonorrhoea], the closer we’re getting to having better prevention options.”
Gonorrhoea is one of the most diagnosed bacterial STIs in the country. The National Notifiable Disease Surveillance System recorded more than 40,000 gonococcal infections across Australia in 2025, with New South Wales and Victoria both reporting more than 10,000 cases each.
