Two people in hotel quarantine in Canberra have returned "weak positive" tests for COVID-19.
ACT Health Minister Rachel Stephen-Smith on Wednesday said the positive tests could be a sign of early infections, or old infections.
She said the two men, one in his 40s and one a teenager, were asymptomatic and would undergo further testing on Wednesday.
They were not from the same family, and neither were known to have had COVID-19 while they were overseas.
"It is possible that these people may have had COVID previously and had a very mild case of it and not even known that they had it," Ms Stephen-Smith said.
"[They could also be] early in their infection and their viral load has only just reached the point where it's detectable."
Ms Stephen-Smith said the pair were among 177 returned Australian travellers who touched down in Canberra on a repatriation flight from Singapore on Monday evening.
Of the passengers, 146 got out at Canberra and were taken to Pacific Suites on Northbourne Avenue, and the remaining 31 flew on to Sydney.
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Ms Stephen-Smith said the risk to passengers on the flight would depend on whether the men tested positive because of old or new infections.
"If it is an old infection, then there's really [a] very tiny, pretty minuscule risk that it would have potentially been infectious on the flight - particularly as they would have tested negative on their pre-flight test," Ms Stephen-Smith said.
"If it is a new infection, that obviously does present a slightly increased risk to those other passengers, and ... we will continue to monitor [the passengers]."
The minister said that, as of last Thursday, about 50 per cent of hotel quarantine workers in the ACT had received a COVID-19 vaccine.
She said that was a "pretty strong take up", given Canberra's vaccine rollout only started last Monday. Ms Stephen-Smith could not confirm how many hotel quarantine workers in the ACT had received the jab as of this week.
The minister said the ACT was responsible for vaccinating about 4000 workers in "phase 1a" of its vaccine rollout and, so far, more than 1300 people had gotten the jab at the Garran Surge Centre.
She said about 2500 workers had booked in to get the vaccine, and authorities would on Wednesday be contacting those who hadn't.
"Of course, it is only week [two] of the vaccination program and this is only the first dose of the vaccine that people will have had, so we're really continuing to rely most heavily on our infection prevention and control," Ms Stephen-Smith said.
"Those are our frontline defences in terms of reducing any potential risk of transmission from people in hotel quarantine, should they have contracted the coronavirus, to our frontline staff."
The minister reiterated that the ACT would be given an initial 2800 doses of the AstraZeneca to work with, but she said she was still working with the federal government to determine when and where they should be administered, and by what workforce.
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