Auckland could tackle another big Covid-19 outbreak without having to resort to the harsh and heavy measures of a complete level 4 lockdown.
That's according to a new analysis suggesting a regional-scale flare-up can be stamped out under the less restrictive settings of level 3, at similar economic cost.
But it would mean a slightly longer lockdown - and potentially more infections.
While dreaded, lockdowns have proven extremely effective at crushing the coronavirus.
Until now however, it hasn't been fully clear which settings work best for certain outbreak scenarios.
Using data from the first wave of March and April, and the Auckland August cluster which forced the city into level 3 lockdown for nearly three weeks, a team of researchers have compared what might have happened if different approaches were taken.
"With the benefit of hindsight, it is now clear that alert level 3 restrictions can effectively control transmission of Covid-19 - however this wasn't known during the March-April outbreak," said Dr Rachelle Binny, whose analysis with Te Punaha Matatini colleagues has just been published.
Level 4 means people must stay home in their bubbles; schools, universities and most businesses must close; and travel is severely limited for those who aren't essential workers.
Under level 3, people can reconnect with close family and gatherings of up to 10 people are allowed.
Shops can also operate provided there's no close personal contact - even a few days of lost trading can hit many businesses hard - while primary schools and early child education centres can re-open.
Each alert level above 1 came with a heavy economic toll.
For the Greater Auckland region alone, Treasury estimates put the daily costs of levels 4, 3 and 2 at $94m, $57m and $29m respectively.
Auckland Business Chamber chief executive Michael Barnett said the total restrictions of level 4 proved particularly crippling for employers.
"For those days that you can't do business at all, to many small to medium businesses, it's like taking them into a place of death - there's nowhere for them to go."
He was pleased what had been learned this year had allowed authorities to increasingly respond to outbreaks without resorting to the measure.
Still, putting strong measures in place quickly remained crucial to prevent an outbreak rapidly growing out of control.
And, if New Zealand experienced another major and widespread outbreak, Binny said, using level 4 to control the spread would still likely eliminate the virus faster than using level 3.
It also meant fewer infections, and less time before the strong measures could be eased, she said.
"To achieve the same likelihood of elimination, alert level 4 could end up costing less than alert level 3, but only if it is a highly effective alert level 4, such as the nationally-applied measures put in place in the March outbreak."
When it came to regional flare-ups, and rates of transmission similar to what they were at the outset of the August cluster, however, the picture was different.
"A less effective, but perhaps more realistic level 4 - for example one that is put in place only regionally - comes at a more comparable cost to level 3."
For instance, the model showed it would take 23 days under level 3 to eliminate an outbreak involving a median 144 cases, at a cost of $1.84b.
By comparison, the level 4 scenario meant fewer cases - a median 101 - and only required 13 days of restrictions, but still ultimately cost $1.79b.
"So from an economic perspective, alert level 3 may well be the best option for controlling future localised outbreaks, because we now have good evidence that it can control transmission while costing roughly the same as a realistic alert level 4."
Although the modelling didn't factor in longer-term economic costs and social effects, the researchers noted some obvious pros and cons with each scenario.
While life under level 3 meant people could see more of extended family, a longer lockdown period could still pose issues for mental health, family violence and disrupted education.
Binny added that, if alert level 3 was used to control future outbreaks, we all needed to do our bit to ensure the measures were as effective as they'd been in the past.
"That means staying at home as much as possible, maintaining good physical distancing and remembering to keep track of places we've visited using the NZ Covid Tracer app."
The new modelling comes amid news New Zealand's contact tracing systems are about to get smarter.
The Ministry of Health is now in the final stages of getting Apple and Google's jointly-developed, Bluetooth-based contact-tracking system working with the government's official app.
How NZ's early action saved lives
Meanwhile, a separate paper by Te Punaha Matatini modellers explored what may have awaited New Zealand if it stalled in responding to the first wave.
The country moved to alert level 4 on March 25, before dropping back to level 3 on April 27, during a period the country registered just over 1500 cases and 22 deaths.
Nearly 11 weeks later, Covid-19 had been eliminated.
Had the shift to alert level 4 been delayed by 20 days, the country could have recorded more than 11,500 cases and 200 deaths - and slashed the chance of eliminating the virus to just 7 per cent.
The modelling indicated that Māori and Pacific people - who have a greater infection fatality risk - could have been disproportionately affected.
The delay would have also increased the chance of a longer lockdown period being needed to bring down daily numbers to low levels, given that authorities may have still been reporting 35 fresh cases around the time alert level 4 finished.
A much bleaker scenario explored was one where no lockdowns were put in place at all - potentially leading to two million reported cases and tens of thousands of deaths.
Conversely, moving to alert level 4 five days earlier could have resulted in 500 fewer cases, and 10 fewer deaths.