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The first human trial of a new chlamydia vaccine has shown that it is safe and that it triggers an immune response against the bacteria that cause chlamydia. The team behind the work are planning a larger trial to find out if it can protect against the infection.

Sonya Abraham at Imperial College London and her colleagues used a vaccine that has already been tested in animals including mice, guinea pigs and primates. The drug, known as CTH522, is essentially a human-made version of a protein found on chlamydia bacteria, and prompts the immune system to mount a response to the bacteria. The team combined this with one of two adjuvants 鈥� chemicals that boost the response of the immune system.

Thirty-five women aged 19 to 45 were given either the vaccine with an adjuvant or a placebo. Over the course of five months, each person was given three injections in their arm, as well as two nasal sprays in both nostrils.

Every woman who received the vaccine demonstrated an immune response, say the researchers behind the work. And while the volunteers did report some side effects, these were nothing more serious than those associated with existing vaccines, such as soreness at the site of injection, a fever or headache.

It is too soon to tell whether or not the drug will protect against chlamydia. The team are currently preparing for a larger phase 2 trial, which will help determine which doses might be effective. They plan to develop a dosing schedule that matches that of the current HPV vaccine, so the two can be given at the same time.

鈥淎lthough clinical vaccine testing for chlamydia is in its infancy, this trial suggests optimism for the future,鈥� Taylor Poston and Toni Darville of the University of North Carolina at Chapel Hill write in a comment piece on this trial. 鈥淎 vaccine for prevention of [chlamydia] infection would have enormous public health and economic impact.鈥�

If proven to work, the vaccine could help prevent some of the 131 million annual chlamydia infections seen worldwide. Those are just the cases we know about 鈥� three quarters of infections are symptomless, so there are thought to be many more.

This is a problem because one in six infected women develop other infections and pelvic inflammatory disease, which can lead to infertility. Women who get chlamydia while they are pregnant are at a higher risk of miscarriage, stillbirth, or having a premature baby. And over half of babies born to infected women pick up the infection themselves, putting them at risk of pneumonia and conjunctivitis. Infected men can develop inflammation of the testicles.

Chlamydia can usually be treated with a course of antibiotics, but despite increasing availability of both screening tests and effective treatments, chlamydia cases continue to rise. The hope is that a vaccine could help reduce the incidence of infections.