CTH522, an experimental chlamydia vaccine and the first of its kind to ever reach a Phase I clinical trial has been found to be safe and able to provoke an immune response, according to a study published in The Lancet Infectious Diseases journal.

The trial, in which 35 women were randomly assigned to the drug or a placebo, reported zero related serious adverse reactions and the most frequent adverse events were mild local injection-site reactions, which were reported in all participants in the two vaccine groups and in three (60%) of five participants in the placebo group.

The intranasal vaccination was also not associated with a higher frequency of related local reactions, meaning the positive safety results show that the experimental treatment could become a promising early candidate for a chlamydia vaccine.

Peter Andersen, Statens Serum Institut in Copenhagen, Denmark, said in a statement that "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.”

Chlamydia is one of the most common sexually transmitted infections (STIs) in the UK, passed on through unprotected sex and is particularly common in sexually active teenagers and young adults.

The NHS recommends that if you live in England, are under 25 and are sexually active, you should get tested for chlamydia every year or when you change sexual partner.