The time Australians will need to wait for booster shots will be reduced twice in January.
But Opposition Leader Anthony Albanese says the staged approach is because the federal government is behind in the rollout of boosters and didn't have the capacity to scale up quickly.
Health Minister Greg Hunt says from January 4, boosters will be brought forward to four months after the second dose, down from five months currently.
Then from January 31, people can get boosters after three months.
About 7.5 million Australians will be eligible for their booster shot come January 4. This will jump to 16 million at the end of the month once the time frame is dropped to three months.
But Mr Albanese said the government wasn't prepared to carry out the recommended advice despite the changes being heralded by international evidence.
"The only explanation for why (it's staged), if the government and medical experts (say) three months is better than four months, is because of capacity constraints," he said.
"We have known that booster shots would be required for a long period of time."
Chief Medical Officer Paul Kelly said it wasn't feasible to suddenly give 16 million Australians a booster dose over the holiday period.
"When we got to our peak of vaccination, around 2.2 million doses a week, was leading the world on a per capita basis," he said.
"That's what we aim to get to and exceed during January."
Mr Hunt said Australia was 500,000 booster shots ahead of schedule, with the country surpassing two million third jabs given on Friday
States and territories will be able to move ahead of schedule and offer boosters under the shortened eligibility criteria if they are in a position to do so.
Some vulnerable and immunocompromised people will also be able to receive their fourth dose if the new time frames make them eligible.
Mr Hunt said priority would be given to Australia's most vulnerable people and the ones who have waited the longest between doses.
"We know that it's not an immediate thing when the vaccine starts to wear off," Mr Hunt said.
"It's a time based thing and so we will prioritise the ones that are most at risk."
Mr Hunt said the booster also reduced virus transmission.
"Protection is very strong against severe illness, but what we'll see is a much stronger protection against transmission," he said.
Professor Kelly wouldn't speculate on whether the three-month time frame meant Australians would need to line up for four COVID-19 jabs each year.
But he urged Australians to get the jab, saying a rise in intensive care patients in NSW has been made up almost entirely of unvaccinated people with "not even a first dose let alone a booster".
Compulsory mask-wearing is now in place across almost every state and territory as leaders try to limit the spread over Christmas.
It comes as NSW recorded 5612 infections and one death on Friday, while Victoria reported 2095 cases and eight deaths.
High-risk, large public events in Western Australia will be cancelled and dancing has been banned except at weddings after a backpacker tested positive on Thursday and was infectious in the community for a number of days.
Four additional cases were recorded in WA on Friday, one close contact to the original case and three casual contacts who were exposed but don't know the backpacker.
A hostel in Perth's south has been locked down to stop the spread.
Queensland reported 589 new daily infections on Friday, while South Australia had 688, Tasmania 27, the ACT 102 and the Northern Territory 10.