A vaccine against one of the most common sexually transmitted infections (STIs) could be available within the next 10 years after it showed promising results in an early clinical trial.
The first ever trial in humans of a vaccine against chlamydia has shown that it is safe and can provoke an immune response, sparking hopes that it could one day protect against the disease.
Chlamydia is a major global health problem with 131 million cases occurring annually around the world. However, as three out of four people who catch the disease do not have any symptoms the number of cases is likely to be an underestimate.
In the UK chlamydia is the most commonly diagnosed STI, accounting for 218,095 - or almost half - of new diagnoses in 2018, according to figures from Public Health England.
The infection is particularly common in young women and teenagers and it can lead to infertility and chronic pelvic pain.
In the trial, published in Lancet Infectious Diseases, researchers from the Statens Serum Institute in Denmark and Imperial College London tested two different formulations of the vaccine in 35 healthy volunteers.
Fifteen women received a version of the vaccine with added liposomes to boost immunity. And 15 received a vaccine with aluminium hydroxide known for its ability to produce antibodies. Five of the women received a dummy or placebo vaccine.
Both formulations of the vaccine provoked an immune response but the vaccine with added liposomes performed better, producing more antibodies.
The presence of an immune response does not necessarily mean the vaccine will prevent someone from getting a disease so further trials are needed, researchers said.
Dr Helene Juel, clinical development scientist at the Statens Serum Institute and lead author of the study, said: “Studies of antibodies in mice have found that antibodies in the vagina are the first line of defence against chlamyia infection, which suggests they are key to how effective the new vaccine may be.”
Researchers say that vaccination may be the best way to tackle the chlamydia epidemic as national treatment and screening programmes have failed to reduce the number of cases.
Professor Robin Shattock from Imperial College London told the BBC that a vaccine could be ready for widespread use in as little as five years.
"The findings are encouraging as they show the vaccine is safe and produces the type of immune response that could potentially protect against chlamydia.
"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.
"We hope to start the next phase of testing in the next year to two. If those trials go well we might have a vaccine that can be rolled out in around five years," he said.
Peter Greenhouse, a sexual health consultant from Bristol and a spokesman for the British Association of Sexual Health and HIV, said that if the vaccine eventually proved successful it could prove as much of a breakthrough as the human papillomavirus vaccine for preventing cervical cancer.
But he added: "One problem is that an abnormally vigorous immune response against chlamydia is the main factor causing fallopian tube damage in this small group of women. So the researchers would have to be careful that they didn't trigger a damaging response when a successfully immunised person was subsequently exposed to the infection."
A spokeswoman for sexual health charity Brook said: “We'd be thrilled to see a vaccine in the future but it's essential that people continue to use condoms to protect themselves from STIs.”
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