First ever chlamydia vaccine found safe and immunogenic for humans: Clinical trial

London, UK: The first-ever vaccine for chlamydia treatment is safe and capable of provoking an immune response, according to findings from the phase 1 clinical trial. The vaccine to protect people against the common sexually transmitted infection chlamydia has passed initial safety tests and the results of clinical trial have been published in The Lancet Infectious Diseases journal.

Chlamydia, caused by the bacterium Chlamydia trachomatis, is the most common sexually transmitted bacterial infection worldwide. It presents a major global health burden - with 131 million new cases occurring annually. Vaccination may be the best way to tackle the epidemic, as national screening programmes and antibiotic treatment have failed to decrease the incidence. But till date, no vaccines against genital chlamydia have been tested in clinical trials.

Sonya Abraham, Department of Medicine, Imperial College London, London, UK, and colleagues aimed to assess the safety and immunogenicity of a novel chlamydia vaccine based on a recombinant protein subunit (CTH522) in humans based on a prime-boost immunisation schedule.

The randomized controlled trial included 35 healthy women (aged 19–45 years) from London, UK. They were randomly assigned in the ratio 3:3:1 to three groups:

1. CTH522 adjuvanted with CAF01 liposomes (CTH522:CAF01) (n=15);


2. CTH522 adjuvanted with aluminium hydroxide (CTH522:AH) (n-15); and


3. placebo (saline) (n=5).

Participants received three intramuscular injections of 85 μg vaccine (with adjuvant) or placebo to the deltoid region of the arm at 0, 1, and 4 months, followed by two intranasal administrations of 30 μg unadjuvanted vaccine or placebo (one in each nostril) at months 4·5 and 5·0.

The primary outcome was safety and the secondary outcome was humoral immunogenicity (anti-CTH522 IgG seroconversion).

Key findings include:

• 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.


• 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).


• Both CTH522: CAF01 and CTH522: AH induced anti-CTH522 IgG seroconversion in 15 (100%) of 15 participants after five immunisations, 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.

"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," says study author, Professor Peter Andersen, from Statens Serum Institut, Denmark.

"Although the vaccine provokes an immune response, whether this translates into protective immunity remains unclear," write the authors.

"CTH522 adjuvanted with either CAF01 or aluminium 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," concluded the authors.

To read the complete study log on to https://doi.org/10.1016/S1473-3099(19)30279-8