If the vaccine gains approval, it would become the third COVID-19 vaccine on offer in Australia alongside AstraZeneca and Pfizer.

Adjunct Professor John Skerritt, who leads the Therapeutic Goods Administration, told a parliamentary committee on Monday night, an application for the vaccine was expected in the first two weeks of July.

"The main reason for not having submitted the application to us was that Moderna as a company was not established or incorporated in Australia until very, very recently," Professor Skerritt said.

"We expect that it will be a rather comprehensive application, and it may even include an application for young adolescents.

"We believe that it will be relatively straightforward, but we will still give it our full attention."

Currently, vaccines are only approved for people aged 16 and over.

The federal government has an agreement with Moderna to supply 25 million doses.

The Novavax application is further behind and expected to be submitted in September.

Health Department secretary Brendan Murphy said Australia had spent about $7 billion buying and distributing Covid vaccines.

The states have been given projections of how many vaccine doses they could expect to receive throughout 2021.

Lieutenant General John Frewen said there were 2.3 million doses of Pfizer vaccine "on hand" in Australia with a further 3.4 million to be available throughout July.

He said the change to advice around AstraZeneca shouldn't cause "major disruptions" to the already lagging rollout.

"There will be delays for some individuals booked in for AstraZeneca," Lieutenant General Frewen said.

"Some of those individuals may experience delays in accessing Pfizer now as the booking process beds down.

"There may have to be some prioritisation at the local state level about what other cohort might be allowed in over time."

The government's vaccine advisory committee recently updated advice of the AstraZeneca vaccine to recommend it people over 60, placing more pressure on Pfizer supply.

Australian Technical Advisory Group on Immunisation co-chair, Dr Christopher Blyth told the committee there was a one in two million chance of dying from blood clots associated with the vaccine.

He said the benefit vastly outweighed the risk of contracting COVID-19 for people over 60.

Professor Murphy reiterated anyone aged 50 to 59 who has received the first AstraZeneca dose should get the second.

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"The message is very clear to those 3.8 million Australians who have had a first dose of AstraZeneca, as ATAGI and the TGA have advised, the risk is minuscule of getting an adverse event with the second dose," Professor Murphy said.

Professor Skerritt said Australia "jumped on it quickly" when the blood clot syndrome, thrombosis and thrombocytopenia syndrome, first appeared in Australia.

Following the first reports of a case in April, Professor Skerritt said Australia's leading haematologists and experts in thrombosis had helped ensure cases were picked up quickly.

"We're picking up cases earlier on," he said.

"All our hospitals, all our intensive disease physicians are aware of this rare, but important side effect."

"People are presenting early, it is being picked up early and being treated out of an abundance of caution."

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