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Chlamydia Vaccine Passes Safety Test In First Ever Human Trial

3D cells showing chlamydia elementary bodies (in red) close to the nucleus (in purple). Kateryna Kon/Shutterstock

A chlamydia vaccine has been trialed in humans for the first time – and it was a success, with results published in The Lancet Infectious Diseases showing that it is safe and sparks an immune response against the chlamydia-causing bacterium Chlamydia trachomatis.

There is still a long way to go before it can be marketed to the public. Future trials will monitor its effectiveness and establish the correct dosage, but news that it has made it through this first hurdle is promising. 


"Given the impact of the chlamydia epidemic on women's health, reproductive health, infant health through vertical transmission, and increased susceptibility to other sexually transmitted diseases, a global unmet medical need exists for a vaccine against genital chlamydia," study author Peter Anderson from the Statens Serum Institut in Denmark said in a statement.

Two versions of the vaccines and a placebo jab were tested in 35 women to determine its safety and check that it can trigger an immune response. The first formulation contained added CAF01 liposomes to boost cellular immunity, while the second included aluminum hydroxide, which is known to help increase antibody production. 

The vaccine was administered with three injections (on day 0, 28, and 112) and two intranasal boosts (on day 126 and 140). Thirty-two women received all five jabs.

Both formulations caused an immune response, but the one containing extra CAF01 liposomes produced 560 percent more antibodies. It also showed an enhanced mucosal antibody profile and more consistent cell-mediated response profile – the first providing the first line of defense against infection, the second associated with long-term immunity. Thus, it is this version of the vaccine the researchers hope to take to the next stage. 


Globally, chlamydia is the most common sexually transmitted infection (STI), accounting for roughly 131 million new cases every year. It can be transmitted through unprotected sex, even without penetration. 

It is considered a "silent" disease because it so often doesn't present symptoms. Yet, if it isn't properly treated, it can lead to infertility and other serious complications, including ectopic pregnancy, miscarriage, stillbirth, and preterm birth. It can also leave people more susceptible to other STIs, including gonorrhea and HIV. 

The good news is that it can be treated with antibiotics. Yet, despite this option (and the widespread availability of testing), it is still a big public health problem. This is where the researchers hope a vaccine will come in useful. It could provide long-term preventative protection.

There is a long way to go before it can be reeled out on a national level – the biggest limitation at this stage is the small sample size, which may not expose rarer side effects to the vaccine or confirm its effectiveness at protecting against the disease. 


"A vaccine for prevention of C trachomatis infection would have enormous public health and economic impact," Toni Darville from the University of North Carolina wrote in a linked comment.

"Although clinical vaccine testing for chlamydia is in its infancy, this trial suggests optimism for the future."


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