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Genital chlamydia is the most common bacterial sexually transmitted infection (STI) in the world. But although the infection can be easily treated with antibiotics, it can cause an array of health problems, including infertility in women. For years, researchers have been chasing a vaccine for chlamydia in order to break the chain of reinfection — a vaccine that might not be that far away.

According to recent findings reported by researchers at Imperial College London and the Statens Serum Institut in Copenhagen, a vaccine designed for preventing genital chlamydia provoked an immune response.

“The findings are encouraging as they show the vaccine is safe and produces the type of immune response that could potentially protect against chlamydia,” said Professor Robin Shattock, Head of Mucosal Infection and Immunity within the Department of Infectious Disease at Imperial.

“The next step is to take the vaccine forward to further trials, but until that’s done, we won’t know whether it is truly protective or not.”

The randomised controlled trial involved 35 healthy women, who were assigned to three different groups: 15 received a vaccine with liposomes, 15 received a vaccine with aluminium hydroxide, and 5 got a placebo (a saline solution). In total, each participant received five vaccinations over several months. 

Both formulations of the chlamydia vaccine provoked an immune response in all participants, although the added liposomes proved more effective at producing antibodies. Meanwhile, no participant in the placebo group experienced an immune response.

The major issue with chlamydia is the fact that, most often, people carry it but are unaware of the fact, so they don’t seek treatment. About 131 million new cases occur each year, but as many as 3 out of 4 infections are symptomless, so the real number of cases is likely much higher.

If caught early on, chlamydia is easily treatable. However, the infection can cause complications such as inflammation, infertility, ectopic pregnancy, arthritis and even an increased susceptibility to other STIs, including HIV.

“It is very treatable if identified, but as many people don’t have symptoms it can be missed, and the biggest problem is that it can go on to cause infertility in women,” Shattock said.

He added: “One of the problems we see with current efforts to treat chlamydia is that despite a very big screening, test and treat programme, people get repeatedly re-infected. If you could introduce a protective vaccine, you could break that cycle.”

The findings appeared in The Lancet Infectious Diseases.