Stability of Chlamydia pecorum MOMP at 37 °C: suitability for use in delayed-release vaccine implants in koalas (Phascolarctos cinereus).

The koala (Phascolarctos cinereus) is threatened by Chlamydia pecorum, an obligate intracellular bacterium that causes disease and infertility. Vaccination offers an alternative to antibiotics, and we have developed a safe, immunogenic vaccine that has shown promising results in captive and wild koala populations. However, the current vaccine requires a booster dose to achieve optimal immune protection. A delayed-release implant delivering the booster after primary vaccination could remove the need to recapture wild koalas. For this strategy to succeed, the antigen must remain stable at 37 °C until release. In this study we have assessed the stability and antigenicity of the Chlamydia pecorum major outer membrane protein (MOMP) antigens used in the vaccine after six weeks at 37 °C. In vitro analysis showed that aged MOMP induced antibody responses comparable to unaged antigens. These findings indicate that MOMP retains structural integrity and antigenicity, supporting its suitability for delayed-release vaccine delivery systems.