Finance Minister Mathias Cormann has defended the controversial decision to base budget forecasts on the availability of a coronavirus vaccine.
Tuesday's federal budget will be built on the assumption a vaccine is made available next year, despite warnings the drug may not be effective or widespread enough to bring the economy back to normal.
Senator Cormann said there was a strong likelihood of a vaccine at some stage in 2021.
"If information changes, assessments change," he told reporters in Canberra on Monday.
"But at any one point in time, estimates are based on the best available information and advice in front of us at that point in time."
The budget numbers will be blown out of the water if a vaccine does not come to fruition.
Shadow treasurer Jim Chalmers is waiting to see the financial forecasts before casting judgement.
But he pointed out the budget update in July was based on the assumption international borders would reopen in January and Melbourne would not be locked down a second time.
"It was based on a whole lot of rosy assumptions which fed the prime minister's absurd assumption that the economy would come roaring back to life in the last weekend of September," Dr Chalmers told reporters.
"We always said that was a ridiculous assumption that was being used. The government doesn't have a good record on anticipating what's going on in the economy."
Senator Cormann on Friday released $808.8 million to the health department for initial payments to vaccine developers in Australia and overseas.
"A vaccine is entirely material when it comes to our future economic fortunes," the minister said.
