Australia has just taken a historic step to protect one of its most beloved animals. For the first time in the world, regulators have approved a vaccine to shield koalas from chlamydia, a bacterial disease that has been silently pushing these marsupials toward extinction.
The illness, which spreads through mating, birth, or even a mother’s feces-like digestive substance called pap that joeys (baby koalas) eat, can cause blindness, infertility, urinary tract infections, and even death.
In some wild colonies across Queensland and New South Wales, infection rates reach as high as 70 percent. With koalas already endangered in these states due to habitat loss and climate change, this breakthrough could help save them from vanishing completely by 2050, a timeline scientists once feared possible.
“Some individual colonies are edging closer to local extinction every day, particularly in South East Queensland and New South Wales, where infection rates within populations are often around 50 percent and in some cases can reach as high as 70 percent,” Peter Timms, lead researcher and a microbiology professor at the University of Sunshine Coast, said.
A life-saving single dose
The vaccine is the result of more than 10 to 15 years of work. Researchers faced a tough challenge. Antibiotics could treat chlamydia, but often harmed koalas more than they helped, since they destroyed the gut bacteria that these animals need to digest eucalyptus leaves, their only food. Without eucalyptus, koalas would starve, so a different solution was needed.
After years of testing, the scientists developed a single-dose vaccine that works by training the koala’s immune system to recognize and fight Chlamydia pecorum. The vaccine includes proteins from three strains of the bacteria, along with an adjuvant, a substance that boosts the body’s immune response.
This clever formula means the vaccine not only lowers the chance of infection but also prevents disease from getting worse, and in some cases even reverses symptoms in already infected animals.
Field trials proved promising. Hundreds of wild and captive koalas were vaccinated, and the results showed that it reduced the risk of developing symptoms during breeding age and cut mortality by at least 65 percent. These results suggest that colonies that once faced collapse now have a stronger chance of survival.
“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.
The Australian Pesticides and Veterinary Medicines Authority officially approved the vaccine for use in June 2025, allowing veterinarians and wildlife hospitals to roll it out widely until at least 2027.
The future of koalas is still uncertain
The approval is a huge milestone, but it is not a silver bullet. Conservationists point out that apart from chlamydia, koalas face multiple other threats, including bushfires, urbanization, and above all, the destruction of their eucalyptus forest homes. So even with a vaccine, koalas will still be at risk if they have nowhere to live.
Some critics, like members of the Australian Koala Foundation, also argue that it will be almost impossible to vaccinate the entire koala population. So instead of spending millions of dollars on a vaccine, the efforts should focus on habitat protection.
“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. I accept that chlamydia is an issue for koalas, but I also want people to understand that they’re sick because they haven’t got any habitat,” Deborah Tabart, head of the Australian Koala Foundation, said.
Many other experts, however, see the vaccine as an essential tool to ease at least one of the pressures threatening the species. They believe the greatest impact will come when disease prevention and habitat protection are pursued together, giving koalas both healthier bodies and safer homes.
For the researchers, the next step is securing enough funding and building veterinary networks to vaccinate the most vulnerable populations in the wild. If successful, the vaccine could buy koalas precious time while Australia works to save their forests.
