Post-exposure vaccine protection of CTH522/CAF01 against reinfection with Chlamydia trachomatis requires Th1/Th17 but not Th2-immunity.

Chlamydia trachomatis (C.t.) is globally the most common sexually transmitted bacterium with an estimated 131 million new cases occurring every year. There is no licenced vaccine against C.t. Repeated infections are often observed in women, suggesting that natural immunity is only partially protective. It is therefore important to investigate if a vaccine given post exposure, on top of a partially protective natural immunity, can increase protection against reinfection. In mice, an infection leads to robust immunity to subsequent challenges that precludes an investigation of increased protection elicited by a post-exposure vaccine. Therefore, we developed a new animal model where the first infection only provided partial protection against reinfection. Using this model, we show that UV-SvD/CAF01 and CTH522/CAF01 as post-exposure parenteral vaccines, but not CTH522/AlOH, protected against reinfection. As CTH522/CAF01 also reduced the gross pathology score post reinfection, this suggests that CTH522/CAF01 is both protective and safe as a post-exposure vaccine.