A decline in Gunnedah's koala population has made it difficult to find 60 candidates for a new chlamydia vaccine trial.
A team from the University of Sydney has been scouring properties in Millroy, near Gunnedah, but in a week has only caught 30 koalas, instead of the average eight a day.
With less than a week before the team returns to the city, they are now aiming to find at least 10 more and are "searching, searching, searching".
The vaccine has been developed using samples from koalas in the Gunnedah area and is being administered to sick and well koalas to both combat and prevent the disease. They are also being tagged so they can be tracked via radio signal.
The team carrying out the trial is led by zoologist Dr Valentina Mella and veterinary pathologist Dr Mark Krockenberger who say the decline in numbers is "clearly evident" after years of drought and scorching summers.
"We were so spoiled in the past with getting so many animals so quickly. Nobody really expected this. We knew the decline was real but really, it's the first time we're experiencing this. They're not there, they're not around," Dr Mella said.
"I don't think we're going to get to that number . We have to do what we can."
Dr Mella said landholders around the main research property "Dimberoy" had been "really fantastic" about giving them access to find koalas and do radiotracking.
The other good news is that the koalas the team has found are all in better condition than they were in January when the team was faced with the horror of finding remains and koalas close to death.
"Most are in good or really good condition, which means they're eating good food," Dr Mella said.
We knew the decline was real but really, it's the first time we're experiencing this.Dr Valentina Mella
Dr Krockenberger said the recovery of gum trees, thanks to regular rain, was key to the change.
"One animal we had in [Tuesday] was 6kg in January and now it's 8.3kg," he said.
"It was very thin [in January]. That animal was very close to death."
There are still physical signs of chlamydia in some animals but others that appear healthy could also be carrying the disease.
"A lot of animals do have signs of chronic disease. Not that many have signs of acute disease. It's mostly chlamydia," Dr Krockenberger said.
"Our hope with the vaccine is that we can reduce transmission of the organism between koalas. We're hoping they'll remain uninfected and will be able to breed for longer or perhaps their full lifespan. Already affected animals, we're hoping the vaccine will improve their general health but it's not really likely they'll become fertile again."
Dr Krockenberger said another observation was that the koalas were finding were older in years.
"The average age has been going up every year, which means we're not recruiting young animals into the population, so it's on a very bad trajectory in terms of overall population," he said.
"The worrying thing is we haven't seen any evidence of young ... at this time of year, we would expect to see some animals with joeys on the back and expect to start seeing some pouch young of the females.
"[It] really means that our vaccination project is even more important now to see if we can limit the spread of chlamydia and in animals that are breeding, they hopefully won't become infected."
The chlamydia vaccine was designed by the University of Sunshine Coast's Professor Peter Timms.
The vaccinated animals will be monitored over a three-year period and data compared to the koalas that were not vaccinated. The team's next visit will be in six months.
In the meantime, a local couple has volunteered to carry out radio tracking for the university to keep an eye on the koalas.