Chlamydia Vaccine Candidate Presents 100% Four-fold Seroconversion Rate

A vaccine to prevent chlamydia infections is considered an important measure to control sexually transmitted and ocular infections.

Chlamydia trachomatis is the most common sexually transmitted bacterial infection worldwide, says the U.S. CDC.

As of April 2024, there is no vaccine against the major global pathogen Chlamydia trachomatis; its different serovars cause trachoma in the eye or chlamydia in the genital tract. 

However, significant research and investment have been made towards developing a chlamydial vaccine, but it has been quite some time since a successful phase 1 trial, commented Wilhelmina Huston, with the School of Life Sciences, University of Technology, Sydney, Australia, in an editorial published by The Lancet.

According to results from a phase 1 study (CHLM-02), Statens Serum Institut's CTH522, adjuvanted with CAF01 or CAF09b, is safe and immunogenic. 85 μg CTH522-CAF01 induces robust serum IgG binding titers.

Intradermal vaccination conferred systemic IgG neutralization breadth, and topical ocular administration increased ocular IgA formation. By day 42, the active groups had a 100% four-fold seroconversion rate, while the placebo group had no seroconversion.

The participants were healthy men and non-pregnant women aged 18–45 years without pre-existing C trachomatis genital infection.

Participants were randomly assigned (1:1:1:1:1) to each of the groups A–E, which received an investigational medicinal product, and group F received a placebo only.

Two liposomal adjuvants, CAF01 and CAF09b, were compared.

Serum IgG anti-CTH522 titers were higher after 85 μg CTH522-CAF01 than 15 μg, although not significantly, with no difference after three injections of 85 μg CTH522-CAF01 compared with CTH522-CAF09b (group E).

Intradermal CTH522 (group C) induced high titers of serum IgG anti-CTH522 neutralizing antibodies against serovars B (trachoma) and D (urogenital).

Topical ocular CTH522 (group B) at days 28 and 112 induced higher total ocular IgA compared with baseline (p<0·001).

Participants in all active vaccine groups, particularly groups B and E, developed cell-mediated immune responses against CTH522.

These findings published by The Lancet indicate the CTH522 vaccine candidate's regimens against ocular trachoma and urogenital chlamydia for testing in phase 2 clinical trials.

This phase 1, double-blind, randomized, placebo-controlled trial was conducted at the National Institute for Health Research Imperial Clinical Research Facility in the U.K.

As of April 17, 2024, the U.S. FDA, the U.K., and the European Medicines Agency have not approved a vaccine to prevent chlamydia infections.

However, Sanofi's multi-antigen chlamydia vaccine candidate is planning a Phase 1/2 study in 2024.