ANALYSIS:
The move to quickly impose level 4 lockdown in Auckland didn't manage to extinguish Delta, but it helped the city to avoid the fates of Melbourne and Sydney where outbreaks grew exponentially and killed hundreds.
And the ongoing lockdown in Auckland, now well past 100 days, has bought enough time for vaccination coverage to push the growth in daily case numbers back down - though this will likely rise again once the lockdown lifts from Friday.
"All the way through we've been wondering whether we're going to hit one of those big exponential growth curves that hit Melbourne and Sydney," Covid-19 Response Minister Chris Hipkins told the Herald.
"The fact that we haven't is quite a lot of comfort for me."
And such growth isn't on the horizon, he said, given that Auckland's eligible population is now at 93 per cent single dosed and 89 per cent double dosed.
"If you look at where we're at with vaccinations now relative to where they were at when those big surges happened, I think we're really well positioned as we open up."
The outbreaks in Auckland, Sydney and Melbourne have shared many similarities, each starting with Delta spreading through a population with low vaccination coverage.
Each city tried unsuccessfully to eliminate the virus, though lockdowns were continued in an effort to keep health systems from being inundated while vaccination coverage climbed higher.
But the outbreaks in Sydney and Melbourne have each claimed more than 500 lives, while Auckland's outbreak has claimed 18.
A graph compiled by the Ministry of Health shows a starting point for each city when there were 10 new daily cases in the outbreak.
The trajectory rose much more sharply in Auckland than in Melbourne or Sydney, but the level 4 lockdown - imposed after the first Delta case was detected, on August 17 - put the brakes on.
Auckland's lockdown was also considered more strict than Sydney's and Melbourne's.
"One of the challenges in Sydney is that they'd kind of made not having lockdowns a bit of a point of pride early on," Hipkins said.
"And that means that when they did do one, I don't think they had the same degree of goodwill and buy-in that we had when we started ours.
"The fact that we hadn't had those prolonged periods of restrictions prior to the outbreak, I think, certainly helped."
The outbreaks in Melbourne and Sydney started to grow exponentially about 50 days in - more sharply in Melbourne - but at that point in Auckland the number of daily cases was only rising very slowly.
By then Māori, who were and still are the least vaccinated group, had become the most common ethnicity among active cases.
When the Delta outbreak in Auckland did start growing exponentially, it was after the outbreak had spread from marginalised groups to all suburbs across Auckland.
But the growth was much more mild compared to Sydney and Melbourne, and soon plateaued on the back of increasing vaccination coverage, as well as the work of public health officials.
"Probably somewhere around day 95, we started to level off and now we've actually started to dip down a bit," Hipkins said.
But that didn't mean case numbers in Auckland wouldn't start climbing again after Friday, when the lockdown will end and household bubbles will no longer apply.
Covid-19 modellers expect that to happen, but add that it's extremely difficult to say by how much as it would depend on people's behaviour - especially the unvaccinated.
"We head into the unknown, and we have to be prepared for the fact that case numbers could trend up a bit," Hipkins said.
The case numbers are increasing again in Melbourne, driven mainly by outbreaks linked to schools.
This highlighted the importance of the public health measures in schools for the last few weeks before the end of term, Hipkins said.
And by the time they return for the next school year, he is "optimistic" the vaccine will be available for those aged 5 to 11.
Pfizer has indicated that supply of the paediatric version of the vaccine will be available by the end of the year or early next year, he said, and it could then be rolled out in a targeted way.
"We will have the opportunity to look at areas that are hotspots or that have a greater degree of risk associated with them and prioritise those areas for speedy rollout of those paediatric doses."
Day zero in Melbourne was August 6, when Victoria's vaccination coverage for the eligible population (16 and over at the time) was 44 per cent for one dose and 21 per cent for two doses.
Some restrictions were eased 76 days later, as the growth curve plateaued, when Melbourne hit the 70 per cent target for fully vaccinated people aged 16 and over.
Lockdown was lifted for the fully vaccinated in Melbourne on November 19, 105 days after day zero.
For Sydney day zero was June 22 and, like Melbourne, some restrictions were lifted in Sydney when 70 per cent of people aged 16 and over were fully vaccinated, which was 111 days after day zero. By then, its curve had been falling for weeks.
From December 15, restrictions in Sydney will be eased even further with capacity limits for hospitality venues scrapped, along with its vaccine pass, meaning the unvaccinated can enter high risk venues. Vaccination coverage for those 16 and over is expected to be 93 per cent by then.
Auckland started day zero with about a quarter of people aged 16 and over fully vaccinated.
Restrictions were eased when Auckland was moved into level 3, and then into the steps of level 3 following advice from the public health teams on the ground that the risk was not material.
Each easing of restrictions drew concern about the impact it would have particularly on young Māori, but the growth curve has not risen sharply on the back of extensive efforts to vaccinate those populations in recent weeks.
Looking ahead, Hipkins said the Government had a proactive campaign to reach those receiving mental health and addiction support, where vaccination coverage is far behind the general population.
According to data platform Tūtohi, only 66 per cent of eligible people receiving such support are double dosed, while 79 per cent have had one dose.
The NZ Needle Exchange Programme has said getting support to take vaccinations to their clients has been a "postcode lottery", with some DHBs being much better than others.
"There is a very active campaign amongst users of drug and alcohol services right now, and it has been happening for a couple of weeks off the back of what we've seen in this latest challenging period," Hipkins said, referring to cases in Auckland and Waikato.
It follows concerns about use-of-force powers being given to staff.