An existing meningitis vaccine offers protection against gonorrhoea, three studies said on Thursday, pointing towards a new way to fight the spread of the sexually transmitted disease.
Sometimes called "the clap", gonorrhoea infected around 82 million people last year, according to the World Health Organization.
The number of cases has been rising as resistance grows to the drugs used to treat the disease, leading to fears it could become increasingly untreatable.
No vaccine has been developed for gonorrhoea, which mainly affects people under 30 -- particularly men -- and can only be avoided by using a condom or abstaining from sex.
However, three new studies in the Lancet Infectious Diseases journal show how effective a vaccine against fellow bacterial infection meningitis B could be against gonorrhoea.
Australian researchers analysed the data of more than 53,000 adolescents and young adults who received the two-dose 4CMenB meningococcal B vaccine in the state of South Australia.
They found that while it was highly effective against meningitis and sepsis, it was also 33-percent effective against gonorrhoea.
Helen Marshall of the Women's and Children's Hospital in Adelaide, who led the study, said the findings were "vital to inform global meningitis vaccination programmes and policy decisions".
Another study carried out in the United States found that two vaccine doses provided 40-percent protection against gonorrhoea, while one dose offered 26 percent.
The study, led by Winston Abara of the US Centers for Disease Control and Prevention, examined the health records of 110,000 16- to 23-year-olds in New York City and Philadelphia from 2016 to 2018, comparing gonorrhoea and chlamydia cases with meningococcal vaccination rates.
Both sets of authors acknowledged limitations in their observational studies, calling for clinical trials to confirm the results.
Such trials could "also offer important insights towards the development of a vaccine specifically for gonorrhoea", Abara said.
A third study in Britain used modelling to look at the health and economic impact of using the vaccine against gonorrhoea.
The researchers estimated that a vaccination campaign targeting men who have sex with men in England would prevent 110,000 cases and save eight million pounds ($10.4 million, 9.6 million euros) over a decade.
Gonorrhoea spreads easily because many carriers are unaware of their infection and unwittingly pass it on to new sexual partners.
Left untreated, it can cause infertility in both genders and increases susceptibility to contracting HIV.