(CNN) Scientists have taken a step towards a vaccine for chlamydia following a successful early trial.

A vaccine developed by a British and Danish team was shown to be safe and effective during a randomized controlled trial involving 35 women, according to a study published in medical journal The Lancet Infectious Diseases

Chlamydia is the most common bacterial sexually transmitted infection (STI) in the world. There are 131 million new cases every year, according to Imperial College London, with as many as three-quarters showing no symptoms. However it can cause infertility if left untreated.

The researchers, from Imperial College London, UK, and the Statens Serum Institut (SSI), Denmark, acknowledge that the development of the vaccine has a long way to go. It had however produced the immune response they had hoped for, and none of the women developed any serious side effects.

"The most important result is that we have seen protective antibodies against chlamydia in the genital tracts," said study author Frank Follmann of SSI in a statement.

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