While an anti-fertility drug in bait form could be available in the next 10 years, the ACT government will still use firearms to help control the abundance of eastern greys in Canberra.

But ACT Parks and Conservation Service director Daniel Iglesias said these culls would only occur ''every now and then'' to bring the number of kangaroos down to a sustainable level to vaccinate.

He said he would also expect the total number of kangaroos culled each year to decrease.

''We understand that to use firearms is a clumsy way of achieving population control and it would be great if we could find an alternative so we could have an extra bow with our quiver if you like,'' he said.

Mr Iglesias said the critical issue was that the vaccine could only be administered by injection.

''So we've got the same problem, we've got to catch them all,'' he said. ''We'd be here for 150 years and all the while there's animals coming in from other areas so it's just not feasible.''

The ACT government has been investing in the development of a long-term vaccination for kangaroos for more than a decade.

Culling is the only other option considered to be appropriate for controlling the transient population in the ACT.

Research officer Claire Wimpenny said the most recent trial had shown positive indications for a successful vaccination.

In 2008 15 kangaroos were given the injection and a further 10 were given the same needle without the vaccination's active ingredient. Those kangaroos given the active vaccination have not bred for three cycles while those given the ''sham'' shot have reproduced.

''The hope is that these can be developed into some sort of oral bait, which is something the ACT could really use,'' Ms Wimpenny said.

She said it would be at least another decade before a bait form of vaccination would be available.

The ACT government is culling about 2000 eastern grey kangaroos across nine nature reserves.