An early-stage clinical trial has come back with promising results for a chlamydia vaccine, researchers have said.

There is currently no jab to protect against the disease, which is one of the most common sexually transmitted infections (STIs) in the UK.

Almost 200,000 cases were identified in England alone in 2022, a nearly 25% rise from the year before, according to latest NHS figures.

Chlamydia is a common cause of infertility in women. It can cause pelvic inflammatory disease, which can lead to scar tissue which makes it harder to get pregnant if left untreated.

The bacteria can also cause an eye infection that is responsible for vision loss in 1.9 million people worldwide, according to the Centers for Disease Control and Prevention in the US.

An early clinical trial of the experimental vaccine, led by researchers in the UK and Denmark, found it was safe and induced an immune response, according to findings published in The Lancet Infectious Diseases journal.

More than 150 people took part in the study between 2020 and 2022 at the National Institute for Health Research in London.

Participants were equally split between healthy men and women with an average age of 26. None of them had chlamydia.

The researchers tested several different dosages of the vaccine, and participants got either the jab or a placebo on three separate days over a period of almost four months.

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Although the vaccine induced an immune response, Dr Hilary Reno, medical director of the St Louis County Sexual Health Clinic, said questions remained about its effectiveness.

She said: “Does it confer the ability to hold off infection with chlamydia? If you do have an infection, does it mean you’re more likely to have an asymptomatic infection?

“We don’t know that and that’s what the next phase of studies would be.”

The researchers are now planning to launch a larger, “phase two” trial that would look at the vaccine’s effectiveness.

The hope is that one day the jab will be able to prevent both infections in the reproductive system, as well as in the eyes, said Jes Dietrich, a senior scientist at the Statens Serum Institute in Denmark and a lead author of the study.

In addition to a shot in the arm, participants in the study also received a vaccine in the form of an eye drop.

“I was very pleasantly surprised because it’s really difficult to induce immunity in the eye,” Dr Dietrich said.

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David Harvey, executive director of the National Coalition of STD Directors in the US, said the vaccine was “desperately needed”.

One of the other most common STIs is the Human Papillomavirus (HPV), although most people with the virus have no symptoms.

Some strains are associated with cervical cancer and the UK has been offering all secondary school girls an HPV vaccine since 2008.

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