Australia's COVID-19 vaccine rollout has passed another milestone, with 50 per cent of children aged five to 11 having received their first dose.

The figure was reached on Monday, with more than 1.1 million children in the cohort being vaccinated.

The vaccine rollout for young children started in early January and the age-group halfway mark comes days after a second type of inoculation was approved for children.

Australia's leading advisory group for immunisations gave the green light last week for Moderna to be used as a COVID-19 vaccine for six to 11-year-olds.

Australia was the first country in the world to approve the Moderna vaccine for children. It joined Pfizer as an eligible COVID-19 jab for children.

While more than 50 per cent of five to 11-year-olds have received their first dose, less than one per cent have been fully vaccinated.

The head of Australia's medical regulator John Skerritt said last week children under the age of five would likely not be be approved for a COVID-19 jab until well after Easter.

Professor Skerritt had indicated approvals by US regulators had been "put on ice".

It comes amid reports the federal government is potentially considering receiving a fourth COVID-19 vaccine and a flu jab at the same time, ahead of a predicted winter surge in cases.

Such a plan would be dependent on the Australian Technical Advisory Group on Immunisation giving approval.

A federal health department spokeswoman told AAP that ATAGI was constantly examining vaccine data.

"ATAGI continues to monitor evidence emerging from medical research on the effectiveness of the COVID-19 vaccines both locally and internationally," the spokeswoman said.

"ATAGI will update its advice and recommendations accordingly."

Meanwhile, more than 11.4 million booster doses have been administered across the country, or more than 63 per cent of the eligible population aged 16 and over.

Health Minister Greg Hunt also confirmed on Monday more than 54 million COVID-19 vaccine doses had been administered since the start of the rollout last year.

Ahead of its hard border reopening to the rest of the country this week, Western Australia registered its highest daily total of COVID-19 cases, with 1114 new infections.

The state's border will come down on Thursday, after months of being isolated from eastern states.

A further 12 COVID-deaths were reported on Monday across the country.

Of those, six were from NSW, three in Victoria, as well as one in Queensland, South Australia and the ACT.

There were more than 18,000 new infections detected nationally in the latest reporting period.