Queensland and the Northern Territory have hit the 80 per cent vaccination mark, as Deputy Prime Minister Barnaby Joyce, travelling overseas, tested positive to COVID-19.
Mr Joyce said in a statement he tested positive for the virus while on a work trip to Washington DC.
He said he had been experiencing mild symptoms and chose to get tested.
All other members of the delegation travelling with Mr Joyce have tested negative.
Mr Joyce will remain in isolation in the US until further advice is received.
Speaking to ABC Radio, Mr Joyce said all necessary precautions were being taken.
"I'm very frustrated that I will be locked up in a room for 10 days, but that's part of the process," he said.
"We arrived here from England and I chose to get a test and tested positive and all my colleagues tested negative - the luck of the draw I suppose."
Mr Joyce said he had been tested for COVID-19 twice while he was in the UK, and had recorded negative results then.
Meanwhile, Queensland and the NT both reached the milestone of 80 per cent of residents over 16 being fully vaccinated.
Prime Minister Scott Morrison confirmed both jurisdictions had reached the mark, ahead of the full release of the latest vaccination statistics later on Thursday.
Western Australia is now the only state or territory not to have reached the 80 per cent mark.
Nationally, more than 88 per cent of over 16s have been fully vaccinated while 93 per cent have had their first dose.
As more cases of COVID-19 associated with the Omicron variant emerge, the World Health Organisation has urged countries not to be complacent with regards to the new strain.
WHO spokeswoman Margaret Harris said while work was being undertaken to investigate the severity of Omicron, people should be alert.
"We are saying take all the measures seriously now, whether its Delta or Omicron - we can't be relaxed right now," she told ABC Radio.
"There's such an inequity in the distribution of vaccines, we have populations that are still exposed, and we've got highly vulnerable people in those populations."
Meanwhile, a new study showed the Pfizer vaccine booster was an effective defence against the Omicron variant, despite the initial two doses being less effective.
Vaccine expert and chair of the Coalition for Epidemic Preparedness Jane Halton said Omicron would become the dominant variant in Australia and was here to stay.
"It's arrived and we're now seeing it spreading not just in Sydney but elsewhere," Ms Halton told the Nine Network.
"I think the horse has bolted."
More than 580,000 adults have received a booster shot.
Australian medical regulators have also granted provisional approval to the Moderna vaccine to be used as a booster.
A final decision on approval from Australia's leading vaccine body is expected next week.
There were 420 new infections in NSW reported on Thursday, along with one death.
In Victoria, the state had 1232 cases and nine fatalities.
Queensland also confirmed two cases of Omicron in people from overseas on Wednesday.
Meanwhile, the ACT recorded eight new COVID-19 infections and one more death.
A baby girl was among two new cases in the Northern Territory.
Australian Associated Press
