Australian scientists have begun vaccinating wild koalas against chlamydia in an ambitious field trial in New South Wales.

The aim is to test a method for protecting the beloved marsupials against a widespread disease that causes blindness, infertility and death.

“It’s killing koalas because they become so sick they can’t climb trees to get food, or escape predators, and females can become infertile,” said Samuel Phillips, a microbiologist at the University of the Sunshine Coast who helped to develop the vaccine.

The scientists’ initial goal is to catch, vaccinate and monitor around half of the koala population in the Northern Rivers region of New South Wales — that means vaccinating around 50 animals.

The safety and effectiveness of the single-shot vaccine, which has been designed specifically for koalas, has previously been tested by vaccinating a few hundred koalas brought to wildlife rescue centers for other afflictions.