First chlamydia vaccine shows early success

The first experimental chlamydia vaccine to ever reach a phase 1 clinical trial has been shown to be tolerably safe and to provoke an immune response, according to a recent study published in The Lancet Infectious Diseases.

The vaccine, known as CTH522, was administered as an adjuvanted intramuscular vaccine and an unadjuvanted intranasal vaccine booster. Results showed that, aside from some mild local injection-site reactions, the intramuscular vaccine was mostly safe with no serious adverse-related events. The intranasal vaccine was not associated with a higher frequency of local site reactions.

Both vaccines induced an anti-CTH522 seroconversion immune response in all participants, whereas no seroconversion was seen in the placebo group. The formulation of CTH522 adjuvanted with CAF01 liposomes showed a more consistent immune response than CTH522 adjuvanted with aluminium hydroxide, making it a candidate for future development.

The trial was carried out at Hammersmith Hospital, London, by researchers from Imperial College London and the Statens Serum Institut, Denmark. In it, 35 healthy female volunteers, aged 19–45 years and without chlamydia, were randomly assigned to receive one of the two formulations of the CTH522 vaccine, or placebo. Safety was the primary outcome, with humoral immunogenicity the secondary outcome.

Chlamydia is the most common bacterial sexually transmitted infection in the world, and vaccines are being investigated as a novel treatment option to mitigate against antimicrobial resistance.

Peter Andersen, Statens Serum Institut in Copenhagen, Denmark, said in a statement: ‘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.’

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