Debate over koala chlamydia vaccine efficacy intensifies after data error claim

Koala populations across eastern Australia suffer high rates of chlamydia, a disease that can cause infertility, blindness and severe weight loss. After more than ten years of research, a single-dose protein vaccine was approved by the Australian Pesticides and Veterinary Medicines Authority in September 2025. However, a pre-print by Keith Chappell and Michaela Blyton uncovered a data-analysis error that had inflated survival benefits, and after correction the study found no significant difference between vaccinated and unvaccinated animals.

Researchers note that antibiotic treatment often disrupts the koalas’ essential gut microbes, and earlier vaccine trials have produced immune responses that did not translate into reduced disease. A biodegradable implant delivering a second dose is being tested, but it has not yet received regulatory approval. The APVMA stresses that the permit only allows a qualified claim about reducing clinical signs and will assess any new scientific findings.