More than 14,000 winter booster doses have been administered since the rollout began this week.
The rollout of the fourth COVID-19 vaccine dose, or second booster, to elderly and vulnerable Australians began on Monday, ahead of a predicted surge in infections during winter.
The head of Australia's vaccine rollout, Lieutenant General John Frewen, told a Senate estimates hearing on Wednesday there had been 14,300 winter booster doses given in just the first two days.
There were 6600 doses administered on Monday, with a further 7700 given out on Tuesday.
However, Lt Gen Frewen told the hearing more people over 65 had already received their fourth dose before the Monday rollout due to being immunocompromised and needing an additional dose in their initial course.
He said more than 100,000 winter doses had been given as a result, with more than 60,000 of those being to people over 65, while there have been 1696 doses given to Indigenous Australians over 50.
The rollout head said more than one in 10 people were overdue for their first booster shot.
Estimates was told more than 11 per cent of the eligible population had yet to receive their third dose of a vaccine.
Lt Gen Frewen said there had been a range of reasons why some people were shunning the booster take-up.
"There is both elements of some confusion and elements of some complacency," he said.
"It comes (down) to people no longer as fearful of Omicron as they were with previous variants. People have had it and have moved on and thought, 'no big deal'."
Latest vaccination figures show more than 94 per cent of those in aged care - and more than 90 per cent of those over 70 - have had their first booster.
Lt Gen Frewen said Australia was ranked 22nd out of OECD countries for the booster rollout.
He told estimates the rate was due to the booster rollout starting later than other countries and nations using different metrics for the rollout.
Australia's OECD ranking for two doses is fifth.
"Originally we were much lower down the OECD rankings for two doses, and as our rollout has proceeded, we've climbed right to the heights," Lt Gen Frewen said.
"We will see that through the booster program as well."
Despite the potential for a surge in COVID cases in winter thanks to new variants, chief medical officer Paul Kelly said Australia was in a good position to handle it.
"While there may be challenges ahead, I see no reason why, even with the easing of restrictions, the strong position in Australia will not likely change over the winter months," he said.
"The 2022 winter season may well present challenges to health systems, healthcare providers, aged care and disability care residents, communities and the economy."
While Professor Kelly said the threat of a new variant was a possibility, Australia would be prepared to handle the situation.
"Work is well under way in all states and territories ... to prepare our healthcare system for the likely co-circulation of COVID-19 and influenza," he said.
"The general principle will be to move away from reducing COVID-19 transmission to protecting people at higher risk of developing severe disease, essentially reducing harm."
LATEST 24-HOUR COVID-19 DATA FROM ACROSS AUSTRALIA:
NSW: 24,151 cases, 15 deaths, 1444 in hospital, 51 in ICU
Victoria: 12,150 cases, three deaths, 331 in hospital, 16 in ICU
Tasmania: 2408 cases, one death, 39 in hospital, one in ICU
Queensland: 8534 cases, one death, 468 in hospital, 14 in ICU
South Australia: 5784 cases, two deaths, 208 people in hospital, 12 in ICU
Western Australia: 8499 cases, five deaths, 259 people in hospital, nine people in ICU.
