The first ever early clinical trial for a vaccine for genital chlamydia has shown it to be safe and effective at provoking an immune response.

The latest findings, from a randomised controlled trial of 35 healthy women led by Imperial College London and the Statens Serum Institut in Copenhagen, demonstrate promising early signs of what could be an effective vaccine against chlamydia.

The infection is the most common bacterial sexually transmitted infection (STI) worldwide and it can lead to infertility.

One of the problems we see is that people get repeatedly re-infected. If you could introduce a protective vaccine, you could break that cycle. Professor Robin Shattock Department of Infectious Disease

The researchers highlight that the work is an ‘important first step’ but add that further trials are now needed to determine whether the immune response provoked by the vaccine will effectively protect against chlamydia infection.

Professor Robin Shattock, Head of Mucosal Infection and Immunity within the Department of Infectious Disease at Imperial said: “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.”

Most prevalent bacterial STI

Chlamydia trachomatis is one of the most prevalent bacterial STIs, representing a major global health burden, with 131 million new cases occurring each year. However, as many as 3 out of 4 infections are symptomless, so the number of cases is likely to be underestimated.

National screening programmes and antibiotic treatment have failed to reduce infection rates, and the highest number of new cases are found in teenagers and young adults.

While infection can often be treated with antibiotics, complications can include inflammation, infertility, ectopic pregnancy, arthritis and even an increased susceptibility to other STIs, including HIV.

Professor Robin Shattock, who led the clinical research at Imperial, says the UK plays a leading role in vaccine research and development. (Image: Imperial College London / Dan Weill)

“The major issue with chlamydia is the long-term consequences,” explained Professor Shattock. “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.”

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.”

Encouraging early results

In the latest trial, researchers compared two different formulations of the new vaccine to examine which would perform better. The 35 women not infected with chlamydia included in the trial were randomly assigned to three different groups: 15 participants received the vaccine with liposomes, 15 received the vaccine with aluminium hydroxide, and 5 received saline solution (placebo).

In total, participants received five vaccinations with three intramuscular injections in the arm over several months, followed by two intranasal boosts.

Both formulations of the vaccine provoked an immune response in 100% of participants, whereas no participants in the placebo group achieved an immune response.

Although both formulations of the vaccine were found to provoke an immune response, the added liposomes consistently performed better and produced more antibodies, so the authors suggest this formulation should be pursued for further clinical development.

The full findings are published in the journal The Lancet Infectious Diseases. The group is now planning phase 2 trials.

UK risks being 'left behind'

The research was made possible through grants from the European Commission. Professor Shattock raised concerns about the future of such international collaborations and whether UK institutions can maintain their leading role in vaccine research.

“Increasingly vaccine development requires multiple partners,” said Professor Shattock. “We have a wealth of world-leading expertise in the UK, with our scientists working to tackle infections, and to discover and develop new vaccines. But if we are no longer part of that European network we may be left behind.

“It’s not just about the funding, it’s about being part of these larger projects that bring together companies and academics and a much wider portfolio of experience, technology and expertise to solve global health problems.”

The clinical trial was carried out at the National Institute for Health Research (NIHR) Imperial Clinical Research Facility.

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‘Safety and immunogenicity of the chlamydia vaccine candidate CTH522 adjuvanted with CAF01 liposomes or aluminium hydroxide: a first-in-human, randomised, double-blind, placebo-controlled, phase 1 trial’ is published in The Lancet Infectious Diseases.

This article is based on materials from The Lancet Infectious Diseases.