Eligible Australians have been reminded to get coronavirus vaccines as soon as possible after four locally acquired cases were uncovered in Melbourne.
Victorian health authorities confirmed on Monday two men, a woman and a child from the same family in the Whittlesea area tested positive.
One of the men had presented to a testing centre when he displayed COVID-19 symptoms.
Chief Medical Officer Paul Kelly told reporters Australia's strong track record containing coronavirus could come unstuck very quickly, particularly with the onset of winter.
"Please don't hesitate to get your vaccine," he said.
Prof Kelly said it was important to look for as many incentives as possible to get people vaccinated.
He is open to novelty measures such as cash lotteries and product discounts seen overseas.
"All of these things are potentially on the table," Prof Kelly said.
"At the moment, we know there is some hesitancy, particularly in the 50 to 69-year-old age group. We are rolling out extremely well in the over 70s. So there is something we need to consider there."
Victorian Health Minister Martin Foley said testing would continue to be vital to tackling the pandemic, as would mask wearing on public transport and using QR codes at venues.
"This is not a time to be complacent," he said.
There are fears the vaccine rollout has been hampered by complacency and concerns among older Australians in relation to the AstraZeneca jab.
The drug has been linked to a small number of extremely rare blood clots.
Despite the remote risk, cabinet minister Simon Birmingham is urging people not to wait for alternative jabs to arrive.
"Australians aged over 50 who have concerns or hesitancy should sit down and talk to their GP," he said.
Prof Kelly has written to all GPs with the latest advice on vaccine side-effects.
He has not joined Department of Health boss Brendan Murphy in blaming sensationalist media reports for the vaccine hesitancy.
One potential vaccine incentive faces stiff opposition.
Scott Morrison wants vaccinated Australians to be able to travel across state borders irrespective of lockdowns.
He will pitch the idea at the next national cabinet meeting on June 4.
But the proposal would also deny freedom of movement to the many Australians who refuse to be immunised.
Premiers and chief ministers are not sold on the interstate passports and neither is federal backbencher Matt Canavan, who says freedom of movement is an Australian birthright.
Labor has dismissed the passport idea as a "thought bubble".
Senator Birmingham said he was focused on keeping domestic borders open rather than responding to closures.
"First and foremost, I want to make sure we keep the borders open by keeping COVID-19 suppressed," he said.
"That is the priority, to make sure the states and territories have no excuse or reason to close those borders.
"It's not unreasonable though to be talking through with the states and territories whether or not those vaccinated Australians are able to move more freely or not."
About 3.6 million doses of coronavirus vaccines have so far been administered across the country, through a mix of AstraZeneca and Pfizer jabs.
The number of vaccinated disability care residents has been revised up to 5888 from fewer than 1000 a week ago.
The overall national number is still well short of what the government was hoping for, but the rollout could soon receive a shot in the arm.
The government is promising two million doses of Pfizer will arrive in Australia each week from the start of October.
This could see every Australian who wants protection from COVID-19 fully immunised by the end of this year.
Australian Associated Press