The vaccine, which has been years in the making, is being trialled at the Australia Zoo Wildlife Hospital in Queensland.

Starting today, about 400 koalas will be given the vaccine.

The trial is of particular importance for southeast Queensland and NSW, where chlamydia affects 50 per cent or more of the koala population.

Male and female koalas contract the disease through sexual contact and mothers can pass it to their joeys as they suckle in the pouch. It can cause eye disease, bladder infections, and worst of all for a species under pressure, infertility.

The University of the Sunshine Coast is leading phase three of the vaccine rollout, after previous phases determined it was safe and produced a good immune system response, therefore affording a good level of protection.

Peter Timms, a professor of microbiology at the university, says koalas admitted to the Australia Zoo Wildlife Hospital will get a single-dose jab after they've been treated and before they're released back into the wild.

All koalas will be micro-chipped, allowing the hospital to record animals that return for any reason over the following year.

Wildlife vet Amber Gillett says chlamydia is the most common reason koalas are admitted to the hospital, and the disease is one of the most significant threats to the species.

"Although many koalas with chlamydia can be treated using traditional antibiotics, some animals cannot be saved due to the severity of their infection," she says.

"Having a vaccine that can help prevent both infection and the severity of the disease is a critical element in the species' conservation management."

As the trials continue, the vaccine is progressing through the government registration process with the Australian Pesticides and Veterinary Medicines Authority.

That should help speed up its manufacture and use if the trials go to plan.

Australian Associated Press