New cases of COVID-19 appear to be plateauing and that's something to take encouragement from, COVID-19 modeller Professor Michael Plank says.
Plank, from the University of Canterbury, told Morning Report case numbers from over the weekend were "roughly" consistent with modelling.
"I think it does look like the numbers are starting to plateau and we can take some encouragement from that," Plank said.
"And one of the things the modelling is showing is that if the numbers are going to come down, if the current settings are sufficient to control this outbreak, we should start to see that happening over the next week.
"The numbers bounce around from day-to-day and I mean it's certainly looking like it is taking a bit longer to get this outbreak under control than we've seen with previous outbreaks.
"That's consistent with what we know about the Delta variant tending to infect everyone in a household. So we expect to see this sort of period with high household transmission.
"But the week ahead really is the crunch week in terms of seeing whether the numbers start to come down."
The length of the tail off was the "big question", he said.
"It's hard to say at this point. I mean, if the lockdown does prove to be really effective at stopping transmission between bubbles, it's possible we could see case numbers down to around 10 per day within the sort of latter part of September, and you know, if we can get down to that level, we'll be in a really good position to eliminate the outbreak."
At least two weeks more in alert level 4 for Auckland was a sensible time frame in which to come back and review how the case numbers were going, Plank said.
"You know it's possible after two weeks that the numbers are coming down quickly to a point that you could start to think about dropping the alert level, but obviously we'll know a lot more when we get there.
As for the rest of the country south of Auckland moving down levels, Plank said "the thing you have to understand is there is a risk of cases leaking out of Auckland and there's essential travel and food supplies.
"Medical supplies have to move around the country so you know while there is a large ongoing outbreak in Auckland, that does create risk of cases popping up in other parts of the country.
"Now, at level 3, we've got a safety net. It means that if the case does pop up, it's not going to be able to grow explosively.
"But I think if we dropped to level 2 that would be risky, and because the case did leak out, it could then cause an explosive outbreak."
Asked if alert level 4 should be tougher given the Delta variant and health workers being at work while infectious, Plank said: "Certainly I think it makes sense to look at where those workplaces are and see if, you know, measures can be improved within the workplace to reduce the amount of contacts between co-workers and reduce the risk of transmission there.
"It would be really good to get clarity going forward on how many essential workers are being infected as a percentage of each day's cases."