A discontinued vaccine used in the past to protect people from meningitis B has been show to offer modest protection against sexually transmitted infection gonorrhoea.
Gonorrhoea, which affects around 78 million people worldwide, is increasingly becoming resistant to antibiotics - to the extent that some gonorrhoea strains cannot be treated with any of the available drugs on the market.
While current preventions strategies do need to be boosted, finding a vaccine for gonorrhoea is also a major public health priority.
The new findings, published in The Lancet, come just days after the World Health Organisation warned that many patients could be left without therapeutic options if no measures were taken.
The struggle to find vaccines
Caused by the bacteria Neisseria gonorrhoeae or gonococcus, gonorrhoea can be transmitted during unprotected sex or if people share sex toys that have not been properly washed.
The bacteria can infect the cervix, the urethra, the rectum, and in some cases the throat or the eyes, with symptoms ranging from the pain while urinating to bleeding and abnormal discharges. However, for many people, the infection is asymptomatic and so they can pass on the infection as they have no idea they have it.
So far, efforts to develop a vaccine against gonorrhoea have been unsuccessful despite years of research. Four vaccine candidates have reached clinical trial stage but none have been shown to be effective.
The new study describe the first vaccine candidate to ever show some kind of protection against the infection.
The scientists analysed the medical data of 14,730 young people from New Zealand aged 15-30. They had been diagnosed with the sexually transmitted infection gonorrhoea or chlamydia, or both. healthy controls was also included in the analyses for comparison.
Among all the participants, some received the MeNZB vaccine during the 2004-06 vaccination programme which was intended to protect them against meningitis B. This vaccine is no longer available today.
An analysis of all the data suggests that vaccinated individuals were significantly less likely to have gonorrhoea than controls (41% vs 51%). Taking into account other factors - including ethnicity, deprivation, geographical area, and gender - the researchers concluded that having previously received the MeNZB vaccine reduced the incidence of gonorrhoea by approximately 31%.
"Our findings provide experimental evidence and a proof of principle that an OMV meningococcal group B vaccine could offer moderate cross-protection against gonorrhoea. This is the first time a vaccine has shown any protection against gonorrhoea," lead author Helen Petousis-Harris from University of Auckland, New Zealand, said in a statement.
"At the moment, the mechanism behind this immune response is unknown, but our findings could inform future vaccine development for both the meningococcal and gonorrhoea vaccines."
Using available vaccines
As Petousis-Harris mentions, scientists are not entirely sure why a vaccine intended for meningitis also works against a sexually transmitted infection. Nevertheless, they know that the Neisseria gonorrhoeae bacteria and Neisseria meningitidis bacteria (responsible for meningitis) are genetically similar, hinting to a biologically plausible mechanism.
The study could be a game-changer against gonorrhoea. While MeNZB has been discontinued, the antigens thought to initiate the immune response to gonorrhoea have been included in another more recently developed meningitis B vaccine, known as 4CMenB.
This vaccine may also provide protection against gonorrhoea and could be tested in future trials.
"The potential ability of an OMV group B meningococcal vaccine to provide even moderate protection against gonorrhoea would have substantial public health benefits in view of the prevalence of gonorrhoea, and the increase in antibiotic resistance. If the 4CMenB vaccine, which is currently available in many countries, is shown to have a similar effect to the MeNZB vaccine, then administering it in adolescent immunisation programmes could result in declines in gonorrhoea," co-author of the study, Professor Steven Black, Cincinnati Children's Hospital, concluded.