A recent independent analysis has raised serious doubts about the effectiveness of a vaccine developed to protect koalas against chlamydia, a disease that has significantly impacted the species in Australia. University of Queensland scientist Keith Chappell, who helped develop the Molecular Clamp vaccine technology used in COVID-19 vaccines, led the study that found no evidence the koala vaccine reduces disease incidence or mortality.

Chlamydia in koalas has long been a conservation concern, and the vaccine received nearly AUD 1 million in public funding. The vaccine was created by a team led by Peter Timms at the University of the Sunshine Coast (UniSC), which earlier studies suggested reduced koala mortality by 64 percent and showed promise in decreasing disease rates. Those findings, published in the journal NPJ Vaccines, fueled expectations for the vaccine’s rollout.

However, Chappell and his colleague Michaela Blyton re-examined the original data and identified a critical error in how survival and disease data were analyzed. Their reassessment revealed that pre-vaccination survival data had been mistakenly included in the vaccinated group, artificially inflating the vaccine’s apparent protective effect. Correcting this error, the researchers found no significant difference in survival or disease rates between vaccinated and unvaccinated koalas.

According to the reanalysis, of 143 vaccinated koalas, 12.6 percent contracted chlamydia, compared with 14.4 percent of 439 unvaccinated animals. Mortality rates were similarly comparable, with 2.1 percent of vaccinated koalas dying versus 2.5 percent in the control group. The study’s authors concluded that the vaccine should not be recommended based on the currently available evidence.

UniSC defended its research team, expressing full confidence in their work and emphasizing that the updated data analysis is still undergoing peer review alongside Chappell’s critique. A university spokesperson noted that independent peer review is a crucial part of the scientific process.

The University of Queensland declined to comment on individual staff matters but acknowledged the right of researchers to express differing scientific opinions under academic freedom.

The Office of the Federal Environment and Water Minister Murray Watt, who previously described the vaccine as historic, said the government would carefully consider findings from the ongoing reviews conducted by the university and external scientific bodies.

In May, UniSC acknowledged that the vaccine’s protective effect against mortality was no longer statistically significant after re-modelling the data with input from Chappell, while continuing to maintain that the vaccine notably reduces disease development. Meanwhile, Professor Timms reiterated at the National Koala Conference in July that the vaccine remains protective and predicted full registration and widespread use by 2028.

Chappell and Blyton’s paper is currently under peer review in NPJ Vaccines, seeking to clarify the chlamydia vaccine’s efficacy and its role in koala conservation efforts moving forward.