Elderly Australians may not be able to get a coronavirus vaccine if the medicine has not been trialled on such an age group.
Department of Health secretary Brendan Murphy said older Australians were considered the most vulnerable and they would be the priority for receiving a vaccine.
"However, most of the vaccines have not been trialled in the over-65s and it's quite likely that the first registrations of some vaccines will exclude them being used in over-65s," Murphy told a Senate estimates hearing on Oct 27.
"So we then have to think about a second level priority."
Other people high on the priority list are health and aged care workers, as well as Indigenous Australians.
Murphy said children would get the vaccine if it's effective at preventing coronavirus transmission.
"We don't immunise children generally to protect them, it's to develop that herd immunity," he said.
An expert committee is developing a range of vaccine strategies taking into account the potential limitations of various drugs.
A vaccine may not prevent transmission but instead prevent severe cases of the disease.
"This is a logistic challenge of the likes we've never seen before, so we are going to need a range of strategies," Murphy told senators.
"We haven't landed all of those plans yet because they're all very complex."
Hospitals and GPs would set up vaccine clinics, while some coronavirus testing centres might be repurposed so they can also administer jabs.
"We're planning to train up a whole army of additional nurses to be nurse immunisers," Murphy said.
Special teams would also be set up to vaccinate aged care staff and residents, if it's deemed safe for older Australians.
If not, aged care staff only may be immunised until a vaccine that's safe for the elderly is available.
Authorities told the hearing on Monday it's likely Australians would need two coronavirus jabs, reiterating it is not known if an effective medicine will be found.