Chlamydia is the most common sexually transmitted bacterial infection worldwide. National screening programs and antibiotic treatment have failed to decrease incidence, and presently there is no vaccine against genital chlamydia tested in clinical trials. Recently, clinical investigators from the UK and Denmark assessed the safety and immunogenicity in humans of a novel chlamydia vaccine based on a recombinant protein subunit (CTH522) in a prime-boost immunization schedule. The team found that CTH522 adjuvanted with either CAFO1 or aluminum hydroxide and appears to be safe and well tolerated. 

The Study

The study was led by Denmark’s Statens Serum Institut (SSI) and collaborator Imperial College of London. They designed this Phase I, double-blind, parallel, placebo-controlled trial of SSI’s adjuvanted chlamydia vaccine CTH522: CTH522-CAF01 [CAF01 is an adjuvant system and CTH522-AI (OH)3.] The study was conducted at Imperial College Research site in the United Kingdom (UK).

The participants were randomly assigned to one of three treatment groups in a ratio of 3:3:1.  The trial consisted of 10 visits and 5 telephonic interviews and involved 35 participants.

The Results

Between August 15, 2016 and Feb 13, 2017, 35 women were randomly assigned (15 to CTH522:CAF01, 15 to CTH522:AH, and five to placebo). 32 (91%) received all five vaccinations and all participants were included in the intention-to-treat analyses. No related serious adverse reactions were reported, and the most frequent adverse events were mild local injection-site reactions, which were reported in all (15 [100%] of 15) participants in the two vaccine groups and in three (60%) of five participants in the placebo group (p=0·0526 for both comparisons).

Intranasal vaccination was not associated with a higher frequency of related local reactions (reported in seven [47%] of 15 participants in the active treatment groups vs three [60%] of five in the placebo group; p=1·000). Both CTH522:CAF01 and CTH522:AH induced anti-CTH522 IgG seroconversion in 15 (100%) of 15 participants after five immunizations, whereas no participants in the placebo group seroconverted. CTH522:CAF01 showed accelerated seroconversion, increased IgG titres, an enhanced mucosal antibody profile, and a more consistent cell-mediated immune response profile compared with CTH522:AH.


CTH522 adjuvanted with either CAF01 or aluminum hydroxide appears to be safe and well tolerated. Both vaccines were immunogenic, although CTH522:CAF01 had a better immunogenicity profile, holding promise for further clinical development.

What is CTH522?

Developed by Statens Serum Institut (SSI), it is a novel vaccine against chlamydia, it is given both as an adjuvanted intramuscular vaccine and an unadjuvanted intranasal vaccine booster. It was mostly safe with no serious related adverse events and only one mild local injection-site reaction reported by Peter Andersen, PhD, of SSI. It is being considered for the first ever vaccine against genital chlamydia.

About Statens Serum Institut 

A Danish research institute set up to combat and prevent infectious diseases, congenital disorders and threats from weapons of mass destruction. Founded in 1902 in the barracks of Artillerivej road, it has now expanded to a much larger research operation and now represents Denmark’s largest research institution in the health sector.


European Commission

The Innovation Fund of Denmark 

Lead Research/Investigators

Sonya Abraham, Imperial College London

Source: The Lancet

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