The second lockdown since the pandemic began was initially slated for one week, but with high-risk exposure sites including schools and a nightclub it quickly became clear that wouldn't be enough.

Another 14 cases were announced on Thursday, but all were linked and just one was infectious in the community but deemed low risk.

Experts say going slow and steady is key to stamping out the highly transmissible Delta strain, which means restrictions would persist for some time.

And, while the virus runs rampant across greater Sydney and parts of regional NSW, there is no guarantee it won't re-enter the territory's porous border.

Professor Adrian Esterman from the University of South Australia said it was critical the ACT didn't act too quickly to ease restrictions while cases remained infectious in the community.

He said it was too early to tell if the outbreak was under control, while the deputy chief health officer Vanessa Johnston was "cautiously optimistic" that the number of people in quarantine was going in the right direction.

Prof Esterman said Victoria lifted its fifth lockdown about a week too soon, when cases were down to about 10 per day and in quarantine.

"Unfortunately, the numbers started building up again. Now, I'm not saying that is because [lockdown was lifted], because we don't know that, but it certainly didn't help," he said.

ACT Chief Minister Andrew Barr has remained adamant a run of no cases in the community - and no mystery cases - would be key to rules relaxing.

Prof Esterman agreed that was the way to go.

"I would like the ACT to at least get down to single digits for the lockdown to end, and all of the cases to be linked," he said.

Prof Esterman said after lockdown, restrictions including a mask mandate, social distancing and capacity requirements would still apply, as has been maintained in states such as South Australia.

"We know the Delta variant spreads very easily by aerosol," he said.

"Breathing in the virus particles that someone else has breathed out, so we know that masks can be incredibly protective."

Large gatherings will also be out for some time to come, as has been foreshadowed by the cancellation of Floriade.

"One of the problems with this SARS-CoV-2 virus is that a small number of people cause most of the infections, and most people who are infected don't cause any infections, or at least one or two," Prof Esterman said.

"So that sort of place where the thing spreads like mad is if you're going into a bar situation where the strain is all around."

A packed nightclub, several schools, and a childcare centre are among nine transmission sites.

These areas are particularly high-risk and therefore the territory had to be particularly cautious, Prof Esterman said.

The ACT will have a "gentle emergence" from lockdown, Mr Barr has said, looking at the situation week by week.

"For the next several months, the entirety of spring, very careful management is going to be necessary," he said on Thursday.

"We have a very delicate balancing act over the next three months to step out safely.

"There remains a high degree of uncertainty about what we're going to face locally and what will play out around us in NSW and across the nation."

Mr Barr has flagged click and collect and delivery services for business would be among the first thing to return.

Life beyond September 2 would be determined next week.

ACT Health released a road map in June of what might happen if there was an outbreak in the city.

The first stage of that plan, "pause and assess", is the lockdown we are living through.

The next step is called "tightening of restrictions" which includes a capacity limit on patrons for all businesses of 20 people.

It would also allow households to have up to five visitors each day and capacity for outdoor gatherings, weddings and funerals would increase.

Thursday marked the two-week "checkpoint" since the first COVID-19 case was detected in Canberra.

Fourteen days is the period when the majority of people who have the virus will stop being infectious.

Prof Esterman said there was about a 5 per cent chance someone could be infectious beyond that point.

"But with 100 people, that's five people," he said.

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"The Delta variant has a median incubation period of four days. That means I get infected and four days later, on average, I start showing symptoms.

"The trouble is that I'm probably infectious a couple of days before I show symptoms. You're getting people who get infected and are infectious within 24 to 48 hours, which is amazing, incredibly rapid."

Vaccination is key.

Mr Barr wants the ACT to aim as high as possible with vaccination, beyond 70 and 80 per cent national targets, to protect the community.

In residents aged 70 and above, first dose vaccination is at 95 per cent.

"That shows what's possible," he said.

Prof Esterman said it was highly likely by the end of the year, we would be dealing with another new strain, one that could be even more complicated and deadly.

"New variants are popping up all the time ... some are much more serious that others," he said.

"I would not be at all surprised between now and the end of the year if there wasn't an even more transmissible and deadly variant than Delta."

We should be prepared, Prof Esterman said, but the good news is that vaccines work against these variants.

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