COVID-19 Response Minister Chris Hipkins has confirmed home-isolation for positive cases is in the works as the Government prepares for the Auckland outbreak to grow.
More than 100 new community cases have been recorded in the past few days despite Auckland's alert level 3 restrictions, but Hipkins on Wednesday confirmed the Government has no plans for a level 4 'circuit-breaker' lockdown as some experts have urged.
"That's not something the Government is considering," Hipkins told reporters.
"The alert level system that we have relies on a very high degree of voluntary compliance of New Zealanders, and what we've seen in those countries that have tried to sustain those kinds of restrictions for a prolonged period of time, they have found that the effectiveness of those restrictions actually diminishes.
"If you wanted to rewind back and say had we stayed at alert level 4 this entire time would we be seeing an escalation in cases, there's a very good chance we'd still be in this position, because the level of compliance and the level of support for alert level 4 can still remain high, but it only requires the small minority who don't follow the rules to increase by a bit and the effectiveness of those alert levels diminishes quite significantly."
Hipkins acknowledged the outbreak in Auckland is growing and it means putting each positive case of COVID-19 into state-run MIQ quarantine is not sustainable.
"As we do see the number of cases increasing, and we are expecting to see the number of cases increasing, the sustainability of putting everybody who is a positive case into quarantine starts to seriously be drawn into question.
"We have been working for some time now on a home-isolation model for positive cases. We've done that before in our first lockdown last year. We did isolate positive cases within their own homes by and large, so we've done this before and we will see that again, and I think we will see that again fairly soon.
"We will still have MIQ for domestic cases where there's a higher degree of risk associated with them. If they can't isolate or we're not confident that they will isolate, we'd still have the ability to use MIQ for those people in order to minimise the risk to the rest of the community."
Prime Minister Jacinda Ardern has already foreshadowed a "doubling in cases".
"At the moment, our modellers have suggested that the R value for this outbreak sits between 1.2 and 1.3, so that does suggest that we will continue to see growth in the outbreak at this stage," she said on Tuesday.
The R value represents the number of people that an infected person will pass a virus on to. Measles has an R number of 15 in populations without immunity. That means, on average, one person would spread measles to 15 others.
The original Wuhan strain of COVID-19 had an R value of 2 to 3 but Delta's R value is about 5 to 6 without lockdown and other restrictions, with some researchers suggesting it's even higher.
Last month Auckland University Professor Shaun Hendy, a disease modeller, said the R value of the Delta outbreak was only about .4, but with Auckland in alert level 3, the virus has spread via food delivery, taxi services and construction workers, thus increasing the R value.
"If we're looking at a value of 1.2 and 1.3, that does see the number of new cases doubling on a fairly regular basis and that does lead you to an exponential growth curve," Hipkins said.
"There's no question, we're going into a period where we are likely to see quite significant growth in the number of cases."
Hipkins denied the Government is ignoring scientific advice.
"It is a science-led response but it's also a science-led response in the context of an increasingly vaccinated population and so we have to recognise that.
"We have to recognise that other countries who have also pursued similar strategies to us around actively running down cases and have continued to do so, have changed their approach in light of higher proportions of their population vaccinated, as we are doing here in New Zealand.
"And we have to recognise no country, sadly, has been able to eliminate Delta and get back to zero. No country has been able to do that. Once Delta is out there, it is much harder to contain, to eliminate, eradicate, than previous strands of the virus."
More than 5 million doses of Pfizer have been administered across New Zealand so far, but only about half the population is fully vaccinated with two doses. Nearly 90 percent of Aucklanders have had one dose, at 87 percent.