Coronavirus hospitalisation numbers in well-vaccinated European nations could be crucial to Australia's decision to restart international travel.
Prime Minister Scott Morrison said the federal government would be keeping a close watch on the rates of serious illness in coming months.
"We will see over the course of this summer in Europe, where a lot of people will be moving around under those new arrangements, and we'll be able to see what the impact of that is," he told Sky News.
Mr Morrison, who is returning from a trip to the UK and France, said hospitalisations were rising in Britain despite high vaccination rates.
"If the virus is there but the hospitalisations and the serious illness don't occur and we see that on a sustained basis, well that says there is a potentially different pathway there," he said.
"But the jury is not in on that yet. New variants like Delta and so on can change all that."
The prime minister signalled a cautious approach to travel would continue with the pandemic still raging in parts of the world.
"It isn't closed one day, open the next."
In May, the government announced that international travel was unlikely to return until mid-2022, other than the trans-Tasman bubble.
However, Australia is also working with Singapore on another potential travel bubble, once vaccination rates are higher.
Victoria's latest lockdown was triggered by health authorities' concern about cases of the Delta and Kappa variants.
Australia has edged past six million doses as the sluggish vaccine rollout continues to gather momentum.
But the portion of the population that is fully immunised remains low, with the latest official figure around three per cent.
In contrast, major European nations are reporting high vaccination rates with the United Kingdom having administered two doses to almost 58 per cent of adults.
Australia's daily data doesn't say how many people have been fully vaccinated.
Labor leader Anthony Albanese said Australia was sitting at 100th in the world for the pace of its vaccination rollout.
"There was an element of complacency last year from the government saying that we were at the front of the queue and will have four million by March," he said.
One in four Australians have received at least one jab after more than 150,000 doses were administered in the most recent 24-hour period.
Health detectives are retracing the steps of a man in his 60s to head off an outbreak in Sydney.
Officials are seeking to find out how the Bondi man - who had not been overseas but transported international flight crews - contracted the disease.
NSW Health was also notified late on Wednesday that a household contact of the man also tested positive for coronavirus.
Exposure sites have been identified across Sydney's east and north, with federal and state health officials meeting on Wednesday night to discuss strategy.
Victoria recorded no new coronavirus cases ahead of restrictions easing further on Friday.
Australian Associated Press