Australia approves world-first single-dose vaccine to protect koalas from chlamydia

Australia’s veterinary medicines regulator has approved a world-first, single-dose vaccine to protect koalas from chlamydia, a disease that causes infertility, blindness and death in the native marsupials and has contributed to steep population declines in parts of the country.

The vaccine was developed over more than a decade by researchers at the University of the Sunshine Coast in Queensland under the leadership of Professor Peter Timms. The research team reported that vaccination reduced the likelihood of koalas developing symptoms during breeding age and cut mortality from chlamydia in wild populations by at least 65%.

With the regulator’s approval, the vaccine can be used in wildlife hospitals, veterinary clinics and in the field to protect populations considered at highest risk, Timms said. He described the single-dose formulation, which requires no booster, as a key feature for use in wild koala populations where repeat administration is difficult.

"We knew a single-dose vaccine — with no need for a booster — was the answer to reducing the rapid, devastating spread of this disease, which accounts for as much as half of koala deaths across all wild populations in Australia," Timms said. He warned that some colonies are approaching local extinction, particularly in southeast Queensland and New South Wales, where infection rates can be around 50% and in some cases reach as high as 70%.

Federal, New South Wales and Queensland governments contributed to the research. Federal Environment Minister Murray Watt said the federal government had supported the vaccine’s development through the A$76 million Saving Koalas Fund and highlighted chlamydia as a widespread threat to koala reproductive health.

Chlamydia infections in koalas can cause urinary tract disease, infertility and blindness. Antibiotic treatment can disrupt the specialized gut bacteria koalas rely on to digest eucalyptus, their sole food source, and can lead to starvation, the university said.

Conservation groups offered mixed responses to the vaccine approval. Deborah Tabart, chair of the Australian Koala Foundation, welcomed attention to disease but said resources should be focused on preserving and restoring habitat. "At the risk of sounding flippant, how can anyone be so delusional as to think that you can vaccinate 100,000 animals? It’s just ridiculous," she said, citing her foundation’s estimate of fewer than 100,000 wild koalas. The government-backed National Koala Monitoring Program estimated last year that Australia’s wild koala population lies between 224,000 and 524,000.

The Queensland Conservation Council, which represents more than 50 environmental groups in the state, described the vaccine as "really good news" and acknowledged chlamydia as a major stressor on koala populations, while also urging stronger protections for koala habitat.

Koalas are listed as endangered in Queensland, New South Wales and the Australian Capital Territory. Habitat loss from wildfires, urban expansion and land clearing, together with climate change and vehicle collisions, are major threats to the species. A 2020 New South Wales government assessment warned that, without concerted action on multiple threats, koalas could face extinction in the state by 2050.

Researchers and conservation authorities say the vaccine is not a standalone solution but a new tool that can reduce disease pressure on vulnerable populations. The approval allows veterinary and wildlife practitioners to begin deploying the vaccine alongside broader conservation measures aimed at protecting habitat and reducing other human-caused threats.