The koala (Phascolarctos cinereus) is an endangered species under threat of extinction from several anthropogenic and natural risks, including disease related to infection with Chlamydia pecorum. For the past 15 years, Australian researchers have been developing a koala specific C. pecorum vaccine that has proven to be safe and effective for up to two years in wild koalas (Phillips et., al 2019). Previous trials were focused on a small region of Southeast Queensland where koala wildlife veterinarians were conducting a koala monitoring program. Five separate trials within this region have resulted in 165 of 680 koalas being vaccinated since 2013 (Khan et al., 2014, 2016a and b, Waugh etal., 2016 and Desclozeaux et al., 2017). For the past ten years clinical examinations have occurred at approximately 6 monthly intervals for all 680 koalas in this region. Analysis of both death in the presence of disease and the occurrence of disease in this large 10-year longitudinal study identified that vaccination significantly increased a vaccinated koalas protection from disease and death due to Chlamydial infection. This analysis identified that protection was not influenced by sex and that the vaccine showed a 65% reduction in disease mortality and a 46% reduction in signs of disease at a 24% vaccine coverage. Furthermore, vaccination was significantly associated with an increase in the koala’s survival.
These findings indicate that vaccination of wild koalas within Australia could result in increased protection against disease and a decreased mortality due to chlamydial disease. Furthermore, these findings also align with modelling data (Craig et al., 2014) that indicates at these levels of effectiveness, koala populations could be recovered from decline within 5 years of vaccinating 20% of a population.