Chlamydia vaccine on the horizon after early clinical trial shows promise

Anne Gulland
A vaccine to protect against chlamydia could be available within 10 years - EyeEm

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 pelvic inflammatory disease (PID) which, in turn, can cause 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 said that if the vaccine had positive results in the next stage of testing it could be available in as little as five years.

He said that a vaccine could have a great impact on the disease. 

"At the moment we have a national screening programme that does prevent people from developing PID but it only prevents about 60 per cent of those cases. With chlamydia you have to know that you're infected - seven out of ten women don't have any symptoms. If you're treated you can still be reinfected.

"If a vaccine worked it should completely prevent infection and mean that you would be immune for a prolonged period of time," he said.

Prof Shattock added that any vaccine would initially be given to teenage girls and ideally administered at the same time as the human papillomavirus (HPV) vaccine, which protects against cervical cancer. 

"Eventually we would like to see it given to boys as well. If you can prevent infection in both sexes you can reduce the amount of chlamydia circulating," 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 be as much of a breakthrough as the HPV vaccine. 

But he added: "Most people that get infected won't be damaged by the infection - they will gradually clear the chlamydia through their own natural immune system clearance. But a significant minority of people - women and men - will mount an unusually strong immune response and that's what causes damage.

"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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