Australians are expected to need two doses of a coronavirus vaccine to be protected against the disease.
But Health Department secretary Brendan Murphy has reiterated that it's unknown if an effective vaccine against the virus will be found.
"Our confidence about the success of vaccines is growing progressively as we see the early trials coming out," he told a Senate estimates hearing on Monday.
"It is unknown but we have to work on the best available evidence."
The Morrison government has put about $2 billion towards a vaccine, with discussions occurring with a number of companies.
"We're expecting that any vaccine that we know about at this stage would require two doses, so that means we require 50 million for the Australian population," the department's associate secretary Caroline Edwards said.
"Of course that depends on all vaccines being safe and effective."
Ms Edwards said if Australia had a surplus of vaccine doses, it hoped to be able to donate or sell them on to other countries.
The government has secured 34 million doses of the AstraZeneca drug to be distributed next year, if the trials prove successful.
It has also struck a separate deal for a drug being developed at the University of Queensland, which is in much earlier stages of testing.
Australia has also signed onto a global coronavirus agreement in the hope of gaining early access to dozens of potential vaccines.
The COVAX facility deal guarantees Australia access to enough vaccine doses for up to 50 per cent of the population.
Officials were mum on how many other companies the government was in talks with, due to not wanting to upset Australia's bargaining position.
Concerns have arisen about potential supply chain issues for a vaccine because they need to be stored at about minus-80 degrees Celsius.
Dr Murphy said US drugmaker Pfizer was looking if the medicine could be stable at a higher temperature.
Australian Associated Press