The Morrison Government does not expect states and territories to reimpose COVID-19 lockdowns despite a worrying surge in infections.
More than 3800 new daily cases have been recorded across NSW and Victoria combined, fuelled by open borders and Christmas travel.
It comes as Deputy Chief Medical Officer Dr Sonya Bennett warns Omicron transmission has a doubling time of around two days.
She urged people to don masks while indoors, stick to outdoor Christmas gatherings and limit numbers.
"I'd probably encourage everyone to think about continuing to wear masks, particularly in settings that are indoor, public indoor spaces that may not be well-ventilated. Think about wearing a mask. It's a simple, easy thing to do.
"The transmission rate alone is concerning. And if we see high numbers, that sheer number of cases is a cause for concern," Dr Bennett told reporters on Sunday.
"If we do end up with a lot of cases, regardless of severity, that's going to clearly have an impact on both business and industry, and individuals."
But Federal Health Minister Greg Hunt did not anticipate a return to COVID-19 lockdowns.
"We're going into summer and we have one of the highest vaccination rates in the world and a very different set of circumstances," he said.
Other countries are ramping up COVID-19 restrictions and the Netherlands is reimposing a lockdown.
"We don't see that that's a likely situation in Australia," Mr Hunt said.
The minister urged people to get their booster shot as soon as they were eligible, five months after a second jab.
About 1.3 million people have received their booster shots, with more than 640,000 doled out in the last week.
Australia has also surpassed a 90 per cent full vaccination rate for people aged 16 and older.
Infectious diseases pediatrician Robert Booy did not expect infections to fall until February following an anticipated January peak.
"There are so many simple things that are effective that could be reinstituted that won't affect people's lives too much," he told the ABC.
Professor Booy wants people to wear masks indoors and for contact tracing to be scaled up, not down.
He also urged NSW to bring back QR code check-ins en masse instead of reserving them for settings classified as high risk.
"There's all sorts of things like that that can be done which can make a difference without having to fully lock down," he said.
NSW recorded 2,566 new infections on Sunday. There are 227 people in hospital, 28 of them in intensive care.
Victoria reported 1,240 new cases and four more deaths. It has 392 COVID-19 patients in hospital, 81 of them in intensive care.
Even if Omicron infections proved to be less severe, Professor Booy warned higher transmission rates meant just as many people could end up in hospital.
