Innovative approach for the clinical development of a Chlamydia trachomatis vaccine through a human challenge model in women.

Chlamydia trachomatis remains the most common sexually transmitted bacterial infection worldwide. Recent phase I trials of the C. trachomatis vaccine candidate CTH522 in women and men have shown that the adjuvanted and non-adjuvanted formulations are safe and elicit systemic (immunoglobulin G) and mucosal (immunoglobulin A) antibodies, as well as vaccine-specific cell-mediated immunity. In advance of a standard phase II randomized controlled trial to determine the vaccine's efficacy, this perspective advocates for a carefully and ethically designed human challenge model as an innovative approach to assess a vaccine's ability to prevent infection and its impact on tubal immunopathogenesis in breakthrough infections. Such models could accelerate vaccine development by providing critical insights, making it essential for stakeholders to consider this approach and expedite the long-awaited chlamydia vaccine.