Experts are stressing that the Government did the right thing by ordering Auckland into lockdown - even if this latest episode proves to have been a short-lived scare.
Cabinet ministers are today set to decide whether current alert levels should be changed or stay in place, with Covid-19 Minister ChrisHipkins just revealing that two further community cases have been confirmed.
Both had a clear link to the initial three cases - a mother, father and daughter from South Auckland - with one being a sibling, and another being a student.
It remained unknown how the original infections occurred - which Covid-19 modeller Professor Shaun Hendy said was critical in the Government's decision-making on Sunday.
"On Sunday, we were looking at a situation that was very reminiscent of the August cluster - so it was exactly right to move to level three.
"Then once we found out we were dealing with one of the more transmissible variants, that was even more important."
Auckland's August cluster quickly grew from a handful of cases to reach nearly 180 - and it took three weeks under level 3 to bring it under control.
"In this case, modelling from multiple angles is telling us that these new variants will be very hard to contain under our current level three, to the point we'd be possibly facing level 3.5, or 4, for a considerable period... at least weeks," Hendy said.
"The fact that we'd gone to alert level 3, that would have stopped it growing - not necessarily enough to eliminate an outbreak of one of these new variants, but enough to put a lid on it while we figure out what was going on."
Given New Zealand had been under the open environment of level 1, with no restrictions on gatherings or movement, and that the UK variant was involved, the potential "R number" - or the number of new cases per infected person - could have been as high as three.
Covid-19 modeller Professor Shaun Hendy said health officials faced a situation like Auckland's August cluster when they discovered the latest community cases. Photo / Greg Bowker
Studies have already suggested the risk of the UK variant had pushed up the "R" value 40 to 70 per cent higher than the original strain - meaning outbreaks could rapidly balloon under exponential growth.
While the original strain typically might infect about 160 cases after five links in a chain, the new variant would typically infect about 1000 cases in the same time.
Of course, the variant, or any other strain of SARS-CoV-2, didn't behave uniformly from case to case.
"We know now that people may infect no one, or just one or two people, whereas others involved in so-called super-spreader events can infect tens, hundreds or even thousands of people," University of Auckland infectious diseases expert Associate Professor Siouxsie Wiles said.
"So with Auckland and the whole country being at a level one, it was quite like being in a melting pot."
In some cases - such as Perth's recent snap lockdown, and last month's Northland scare involving another high-risk variant - big outbreaks fortunately hadn't resulted.
"But in other examples overseas, where there has been rapid transmission through a lot of other people, that hasn't been the case," Wiles said.
"So erring on the side of caution with these cases, we've found, is our best approach."
Where did the lack of further community cases leave decision-makers?
"The unfortunate thing over the last few days is, while we've got some information that is promising, it's not enough to help us really make a call either way," Wiles said.
"The worry is that, right now, if we move back down alert levels, we may have to move up again, given we are still within the incubation period of the virus.
"It will all come down to the Government's appetite for risk, as to what they decide to do."
Otago University epidemiologist Professor Nick Wilson said a specific cause for concern was the fact the daughter in the family of three had displayed symptoms before the mother, whose job's link to the border made her the likelier initial case.
"If the child had been infected first, that would be highly consistent with a potential community outbreak," Wilson said.
"It could have been we were facing something very small, with only a few cases - or it could have been much bigger, with large numbers of cases.
"Having that lockdown in place simply allows us the safety to evaluate the situation more carefully, to make sure things are under control."
He said some countries that had swept out the virus, such as South Korea and Taiwan, had the capability to manage large outbreaks by drawing on vast amounts of contact tracing data.
"Because of concerns about privacy, and because our tracing capability is nowhere near as state-of-the-art as it could be, we really have a lower threshold to go into lockdown."
At the same time, he added, New Zealand had spent little time under lockdown, compared with other OECD nations.
"In terms of restrictions on our freedoms, it has to be said that New Zealand has done amazingly well as a country," he said.
"The evidence keeps building that, not only is this the best health strategy for island countries like ours, it's also the best economic strategy, because it allows the economy to bounce back more quickly."
