Queensland researchers say they have made a breakthrough in the fight to protect the shrinking koala population against chlamydia.

Scientists at the University of the Sunshine Coast said they had successfully vaccinated koalas against the disease, which was responsible for about 50 per cent of the marsupial's deaths.

Researchers said a vaccination could be the key to protecting the native species from the painful and deadly disease.

Koala numbers had dropped dramatically in Queensland, New South Wales and the ACT over the past 20 years.

Microbiologist Professor Peter Timms from the University of the Sunshine Coast in the state's south-east said chlamydia was one of the main reasons for that.

"In females, not only do they get reproductive tract disease which might lead to infertility, but also they get large cysts and they're quite painful," he said.

"You can see the animals that have these cysts and they can die from that.

"As well as that of course, the ones that are infected in the eyes that become blind, it makes it difficult for them to feed.

"In somewhere like south-east Queensland, unfortunately there are wild dogs present and so on."

Professor Timms spent five years working on a vaccine to protect the animals from the disease.

The research team initially tested the treatment on captive koalas with good results.

The next step was to vaccinate 30 wild koalas in the Moreton Bay region, north of Brisbane.

Hope vaccine will improve female koala fertility

Professor Timms said the results were very promising.

The vaccine could be a crucial step towards improving fertility in female animals. ( Supplied: University of the Sunshine Coast )

"The first thing is, animals that are already infected - did it stop the infections going higher or getting more infection load? And the answer to that is yes," he said.

"Second thing is some animals don't yet have the infection but could be going to pick up a new infection so we tested whether or not the vaccine would prevent them from getting new infections."

He said the vaccine could be a crucial step towards improving fertility in female animals to help the population survive.

"None of our vaccinated animals went from having an infection to getting actual disease - so blindness or reproductive tract cysts," he said.

"Whereas in the control group, three of them when from having an infection but then going on to get a disease."

Professor Timms said it would be unrealistic to vaccinate every koala, but it would make sense to treat the hundreds of animals that were processed through care centres and animal hospitals.

"That's an ideal opportunity to vaccinate those koalas while they're already there, before they're released back into the wild," he said.

"But as well as that, there's more and more populations, and the ones we've been doing this trial on in the Moreton Bay region is a good example, where it's humans causing them to be impacted by what we do.

"Those animals can then be captured and potentially the whole population is vaccinated.

"There's plenty of opportunities to vaccinate thousands and thousands of the ones that are most vulnerable at this point in time."

Environment issues impact koala survival

Professor Timms said more effort was needed to protect koala populations that he said were shrinking day by day.

"There are a couple of areas down south of Australia where koala numbers seem to be increasing, and so people think that that means everything's all right," he said.

"The answer is everything's not all right.

"It might be in 10 per cent of the situation it might be okay, but in 90 per cent it's not okay."

He said there were environmental issues that took time to solve.

"You can't turn around tomorrow and at the last minute decide to save them," he said.

"You need to be planning ahead 10 years before their numbers become so low that they're hard to recover again."