Federal Health Minister Greg Hunt has announced Australians will be able to get their Covid booster shots earlier than expected.
Mr Hunt said on Friday morning the period people had to wait between their second and third doses of the vaccine would be reduced to four months from January 4.
This would be reduced further to three months from January 31.
The news comes as NSW's daily Covid infections remain above 5000 and Victoria reported 2095 infections.
Mr Hunt said the decision was made based on advice from the Australian Technical Advisory Group on Immunisation (ATAGI).
The changes announced on Friday means the current eligibility of 3.2 million Australians for the booster will rise to about 7.5 million from January 4.
From January 31, this cohort will jump to 16 million.
Mr Hunt said Australia would hit two million booster shots administered about 10am on Christmas Eve, 500,000 doses ahead of schedule.
"We've had about 1.3 million doses since the expansion of eligibility from six months to five months just over a week and a half ago," the minister said.
Vaccine effectiveness does not disappear 'immediately'
Australia's Chief Medical Officer Professor Paul Kelly said double-dose effectiveness did not just disappear, but "it wanes over time".
"Hence the time-based change in the boosters," he said.
"The positive effect of that is that we do know now that boosters do protect and increase that protection against severe disease once that third dose is given, or a fourth dose in the case of immunocompromised people.
"But I will stress that just because you get to three months or four months or five months or six months, it doesn't mean that you [immediately] will lose that protection... it does decrease over time it remains in place for severe infection, but it is diminished for Omicron compared with Delta."
Prof Kelly said new evidence about Omicron had sparked a rethink about the Covid booster interval.
"We've only know about this [variant] for about four weeks," he said.
"In the last week, in fact last night and the night before, there was more evidence that came around the protective effect of boosters, but also that waning element.
"So the best evidence they've got at the moment is between three and four months essentially [to get a booster], for the reasons of implementation we've gone with the four months... to start."
Meanwhile in NSW case numbers remain high, with 5,612 infections recorded in the 24-hour reporting period to 8pm on Thursday.
One more death has been recorded as hospitalisations rose to 382, with 53 of these in the intensive care unit.
More than 164,000 people have been tested in the same period.
The high number comes as the mandate on wearing masks indoors and QR check-in codes resume in NSW.
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