Australia’s veterinary medicine regulator has approved a vaccine to protect koalas from chlamydia, one of the leading causes of koala infertility and death.

Researchers found the single-dose vaccine reduced mortality in wild koalas (Phascolarctos cinereus) by at least 65%. In some cases, it even reversed existing symptoms in koalas that were already infected.

“Koalas are truly iconic for all of us and sadly their numbers are decreasing,” Peter Timms, who led the development of the vaccine as deputy director of bioinnovation at the University of the Sunshine Coast, Australia, said in a video posted by the university. “This has been a major achievement … after more than 15 years of work and a lot of people contributing to this, we’ve reached this key point.”

Most wild koalas live in eastern Australia’s Queensland and New South Wales states, where the species is listed as endangered. In some colonies, up to 70% are infected by the bacterial strain Chlamydia pecorum, which is transmitted sexually among the animals.

It’s also transmitted from mothers to their babies when they feed them pap, a nutritious feces that allows joeys to digest otherwise toxic eucalyptus, which make up 100% of their diet.

The progression of the disease, Timms added, can be terrible. Eye infections caused by chlamydia can lead to blindness, while urinary tract infections cause infertility and extreme pain.

Antibiotics aren’t a useful treatment because they kill the gut bacteria that koalas need to digest eucalyptus leaves, and without eucalyptus, koalas could starve.

“We know that koalas need help to fight diseases like chlamydia. It’s a widespread threat impacting their reproductive health and causing infertility,” Murray Watt, Australia’s environment minister, said in a statement.

The single-dose vaccine is made up of six different components: the proteins of three different strains of chlamydia and an adjuvant, which enhances the body’s response to the chlamydia proteins. The vaccine offers significant protection without needing a booster.

“We’ve purposely developed a vaccine that only requires one shot,” Timms said “For a wild animal like the koala, that is what you really need.” 

Now that the vaccine is approved, the next step is to secure funding for the rollout, so that veterinary teams can vaccinate at-risk koalas in the field, he added.

Banner image: Lead vaccine researcher Peter Timms with a koala. Image courtesy of UniSC Australia.