Covid 19 coronavirus Delta outbreak: What Auckland needs to exit level 4 lockdown - expert

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The wish list of what Auckland needs to exit level 4 lockdown is simple - ensure there are no mystery cases of Covid, pandemic advisors say.

There were just 11 new Covid cases yesterday as New Zealand remains on track to eliminate the latest outbreak of the virus, Te Pūnaha Matatini Covid-19 modeller Michael Plank said this morning.

The number of people who were infectious while in the community has also been dropping dramatically.

And that meant it's possible Auckland may be able to move down to level 3 restrictions next week, Plank told radio station Newstalk ZB.

However, recent mystery cases - or those cases where health teams don't know how the infected people caught the virus - are still threatening to delay any easing of restrictions.

In particular, all eyes have now turned to two cases who recently took themselves to Middlemore Hospital and tested positive despite having no known link to other people with the virus.

"So there is concern that there could be missing cases we haven't found yet," Plank said.

That meant the priority had now become chasing down the missing links in transmission as fast as possible.

"That will give us confidence there isn't some hidden sub-cluster out there that we haven't managed to find yet," he said.

How that hunt played out over this weekend and into next week would play a key role in any Government decision about easing restrictions, he said.

"It's important to realise, it is not just about the total number of cases," Plank said.

"What also is important is the details of those cases, in particular, are there any unlinked cases, are there any cases that have been infectious in the community.

"So those are the things we'll want to see down to zero for a few days before starting to step down the alert levels."

A decision on alert levels for both Auckland and the rest of the country will be made on Monday.

On Friday, Deputy Prime Minister Grant Robertson said if there happened to be a large number of mystery cases, that could weigh on any alert level decision.

However, he balanced this by saying that if testing was high and case numbers continued to come down, there was some reassurance there were no undetected chains of transmission.

Auckland could move to level 3, while the big question for the rest of the country is whether it could be at level 1, should Auckland remain at level 4.

Plank's fellow Covid modeller Shaun Hendy believed it likely Auckland will stay at alert level 4 for slightly longer.

"At this stage we are probably not popping out on Wednesday morning into level 3," Hendy said, "but it may not be that much further".

Another modeller Rodney Jones said that more time at level 4 was likely to avoid yo-yoing up and down the alert level scale.

"It's kind of a trade-off. You can extend this lockdown further if you come out a bit early you risk going into another moderately long lockdown," Jones said.

The daily case numbers from the pandemic are sending mixed signals.

Case numbers are falling, but they might not be falling fast enough to avoid an extension to Auckland's level 4 lockdown, which is on track to be the longest any part of New Zealand has been under such restrictions since the beginning of the pandemic.

The last time the country moved from level 4 to level 3 - in April last year - it was preceded by nearly a week of single-digit case numbers. Those cases were clearly linked.

This time, new daily cases are still in the double digits.

The country's response is more sophisticated than it was a year ago. The number that keeps officials up at night isn't the number of new daily cases, but the number of cases that cannot be linked to the current outbreak.

Unlinked cases suggest the possibility of wider spreading of the virus, which could lead to new clusters if restrictions are lifted.

The country still has a high number of cases that haven't been epidemiologically linked to other cases in the outbreak.

This number has actually grown over the week. On Tuesday, the number of unlinked cases stood at 24, but by Friday it stood at 29, having cracked 30 the day before.

Hendy said the absolute number of unlinked cases was not necessarily the most important number, as often there was a lag between cases being reported and those cases being linked.

Each day this week a handful of unlinked cases have been recorded but the total number of unlinked cases has risen only slightly, indicating that links are eventually being found - it is just difficult. Bloomfield announced on Friday, for example, that all of the 13 cases announced the previous day had been epidemiologically linked.

The problem is Delta is so transmissible, it appears that anything less than the tightest restrictions is ineffective.

Jones said that even a single case could lead to an outbreak.

"This all began from one limo driver in Sydney that sent Australasia to hell," Jones said.

"The concern has to be that there's a background of infections that we're not getting on top of."