Not since two people returned from Melbourne on July 8 at the height of its second wave and passed it onto three contacts, the last reported on July 10, 2020, has there been a locally-acquired case of COVID-19 in Canberra.

But Canberra's Covid bubble can't last, the ACT chief health officer said. As vaccination ramps up there will be a transition where case numbers rise, Dr Kerryn Coleman said.

The imminent threat of the virus re-entering the ACT from the outbreak of the Delta strain in Sydney has come as a wake-up call for residents, with masks made mandatory for the first time.

There has never been confirmed community transmission, and just one case of 124, who was among Canberra's three Covid fatalities, came from an unidentified source.

Health authorities have maintained the mantra since March 2020 calling for residents to 'do the right thing', and Canberrans have heeded their cry.

While an outbreak of the highly contagious Delta strain forced Greater Sydney into lockdown, and thousands under restrictions in the ACT after travel, still no cases have yet made their way across the border.

ACT Chief Minister Andrew Barr said it was "pleasantly surprising" Canberra had made it through the greatest risk posed this year.

"That's a combination of good management and good luck. Luck can turn, though," he said.

Dr Coleman said there would be a transition period, as vaccination increased where cases in the community would need to be accepted.

"What we want is a level of vaccination where the impact of those cases will not be as severe as we have seen overseas," she said.

"If we want to open our borders and interact with the world again, there will be cases and we'll have to learn to live with cases."

Dr Coleman wanted "nowhere less than 80 per cent" of the population to be vaccinated.

Associate Professor Sanjaya Senanayake, an expert in infectious diseases, said the ACT was a "microcosm", shielded from the risks larger cities faced which put it "one step ahead".

Just five repatriation flights have touched down at Canberra Airport in the past 18 months, a critical factor in Canberra's success.

"That's a huge thing, because if you look at hotel quarantine, there have been about 27 breaches. If we were Sydney, Melbourne, Brisbane or Perth - the risk is obviously much higher than for us," he Senanayake said.

While more than 2100 diplomats and government officials have quarantined at home in Canberra, just five have had the virus, which has been successfully contained.

As a city of universities, federal and territory public servants, diplomats and government officials, Canberra is an "unusually" educated and health-literate population, Associate Professor Senanayake said.

"People know what they have to do, they get tested when they need to get tested. They isolate when they need to isolate," he said.

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For the first time in the pandemic, ACT residents were forced to mask up in most indoor settings for two weeks, in response to the latest outbreak of the Delta variant in Sydney.

Associate Professor Senanayake said there was a benefit for residents who haven't been under yo-yoing restrictions throughout the pandemic.

"Because we're not constantly being told that when we actually do have to do it, we are actually being compliant because we have the enthusiasm and energy to do so," he said.

Australian National University epidemiologist Professor Peter Collignon said with few cases and a "zero-Covid" lifestyle came the risk of complacency. He believed there should be some level of restrictions right across the country, irrespective of community transmission.

"[Winter] is a high-risk period, come three of four months from now we'll be in a much better position because we'll have a lot more people vaccinated, including those under the age of 60," he said.

He said density restrictions in hospitality venues and reduced capacity at stadiums should be introduced until vaccination improved.

"I'd like to see 70 per cent of adults vaccinated, and I think until that time we should, particularly over the next few months, be willing to live with restrictions on all our indoor [activities]," Prof Collignon said.

The ACT has the highest proportion of its population aged above 16 with one dose of the vaccine, at almost 43 per cent.

Across Australia, nearly 32 per cent of people have received one dose of the vaccine.

The Northern Territory has fully vaccinated 18.34 per cent of its population aged above 16 and the ACT 16.21 per cent.

Nationally, 10.18 per cent of the population above 16-years-old is fully vaccinated.

The chief minister said the ACT was was an "above average performer" across jurisdictions.

To date, 181,034 doses have been administered in Canberra, with ACT health authorities working on the assumption 340,000 people were eligible to get the jab.

Associate Professor Senanayake said the ACT benefited from its geography, having a "captive audience" across a small area and had low vaccine hesitancy compared to other jurisdictions.

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