A single-dose vaccine to protect koalas from chlamydia has been approved for use around Australia for the first time, a move wildlife carers say offers hope for a “heartbreaking” situation.
Crucially, no booster shot is required, giving researchers hope that the vaccine can eventually be used in the wild. “It’s difficult to catch a koala once, let alone two or three times,” says Dr Sam Phillips, a microbiologist who has spent almost a decade working on the vaccine.
Phillips says about 50% of koalas have chlamydia, although rates in some wild colonies may be as high as 70%. Combined with deforestation and traffic accidents, the other major threats to the species, he says the disease is “a huge, devastating issue”.
What is changing with the approval of this koala chlamydia vaccine?
After extensive clinical trials treating hundreds of koalas, the veterinary medicines regulator recently gave the go-ahead for wider use nationally, in hospitals, veterinary clinics and in the field.
A spokesperson for the Australian Pesticides and Veterinary Medicines Authority said the vaccine was approved under a minor use permit,which allows registered vets, or people under their direction, to use it.
Which koalas get the jab?
The first batch of the vaccine, expected to be about 500 doses, will be ready to roll out from early 2026. The university’s team wants funding to scale up production to ensure the vaccine can be provided free to more providers.
The plan is not to vaccinate every koala in the national population, which the CSIRO estimates at between 224,000 and 524,000. There aren’t enough doses.
“This would be a vaccine program specific to koalas that are at risk,” Phillips says.
Phillips says the current focus is vaccinating koalas in wildlife hospitals who are already under general anaesthesia for health checks. The hope is to expand efforts to wild populations, but vaccinating wild koalas, including healthy ones, will take time, resources – and highly skilled koala catchers.
“Koalas obviously live high up in trees, they’re not necessarily easy to catch to vaccinate,” Phillips said. Even bringing in koalas found on the ground, which are likely to be already sick or injured, has its challenges. “They’re wild and they’re scared. As far as they’re concerned we’re predators,” says Vickii Lett, koala species coordinator with wildlife rescue organisation Wires.
“If you get a koala that’s really cooperative and doesn’t argue with you when you’re trying to catch it, then you know they’re in real strife,” she said.
How does the vaccine affect the koalas?
The vaccine covers three different variants of chlamydia and uses a unique “triple adjuvant”, an ingredient used to improve the immune response.
The drug, developed by researchers from the University of the Sunshine Coast in partnership with Australian animal health company Tréidlia Biovet, can be given as a single dose, delivered by needle from a qualified vet.
Koalas do not have to be anaesthetised to be vaccinated. Side effects are minor and include swelling around the injection site for a day or two.
Until now, antibiotics have been the only treatment available outside clinical trials, and have to be specially made up. These can also have serious and sometimes deadly side effects. They can kill the koala’s microbiome, which can be fatal if not carefully managed, Lett says. In addition, after antibiotic treatment, once animals recover and are released back to the wild, they can be reinfected.
According to Phillips, research has found the vaccine reduces likelihood of koalas developing symptoms of chlamydia during breeding age, and lowers mortality rates in wild populations “by at least 65%”.
Why are koalas so badly impacted by chlamydia?
It’s unclear how and when koalas first caught the highly contagious disease. Various theories include the possibility it was introduced through infected livestock after European settlement, Phillips says.
Wildlife veterinarian Dr Leanne Wicker says the sexually transmitted disease, which affects both males and females, can be “really nasty”. “Infected koalas can become blind and infertile.”
She says the vaccine’s approval is good news for northern populations especially.
“They’re already suffering significantly from habitat loss, bushfires and the impacts of climate change – we know that their population is dwindling. Chlamydial disease is an additional stress that the population just doesn’t need.”
The severity of chlamydia outbreaks among koalas is worse in Queensland and New South Wales, where the species is listed as endangered.
In Victoria, where there are not enough trees to sustain larger local populations, symptoms are often not as severe. More research is needed to understand the significance of chlamydia for southern populations.
What are the hopes for the koala vaccine?
Lett says the new approval offers hope to wildlife carers. “It’s really hard, especially if you raise joey koalas to put them out there, and then pick them up a few years later when they’re badly affected.”
Seeing affected animals, Lett says, is “heartbreaking”.
Phillips says the vaccine rollout to at-risk koala populations would ideally occur alongside other measures tackling threats such as deforestation, predatory animals and car accidents.
“You would need to go into a population that would be at risk of becoming locally extinct and tackle all of the threats that those koalas are facing.”
We need to remember how fragile the species is, says Lett. “We need to think big picture with them, and think about what we’re doing to their homes.
“I hope things do change, with the help of the vaccine.”