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Modelling by Wigram Capital's Rodney Jones shows the rate of spread is too high for Delta to be eliminated.
Daily cases have been bouncing around in the 20s and teens for the past week and have yet to fall below 10.
Jones has been tracking the numbers virus and says the R value, or the rate it can spread, is still too high and is sitting at 1.
"This is a classic Delta outbreak where you just can't catch up with it, you're always chasing it down but you never catch it," he said.
"There's always cases in the background in the community and they pop into view and threat creates the numbers that we see."
However, Dr Ashley Bloomfield told Morning Report there were too few case numbers to model the rate accurately.
Modelling seen by his team showed the R value was around 0.4 a couple of weeks ago, showing the alert level 4 was doing it's job, he said.
"When you've got so few cases at this point in the outbreak, you can't really model the R value anymore," he said.
"It's most useful early in an outbreak when you've got the numbers going up and then when they're levelling off and starting to come down."
The R value isn't so important in this situation, he said, what is important is whether there are cases being found.
"The vast majority of our cases are now inside households, people isolating, or in quarantine already. Any new cases are the ones that we investigate fully just to find out whether there's other cases out there, and hence the really intensive testing in those seven suburbs, Clover Park being the eighth one added, and a great response there from people yesterday, keen to see more testing there today."
Bloomfield said he doesn't think a level 1 scenario with Delta necessarily means a series of zero cases.
He said now that they were on top of the outbreak, health officials were aiming to get the vaccination rate over 90 percent.
"That's absolutely our new means whereby we will be able to get back to the freedoms we had under level 1, and we're all keen to do that," he said.
"We may not get back to zero, but the important thing is we're going to keep finding any infections and basically continue to contact trace, test, isolate people so that we stop the virus circulating in the community, and that is the aim.
"Everyone recognizes, including the modellers, that it [the vaccination rate] needs to be north of 90 percent for us to be really comfortable that we can open up to the sort of freedoms, we had in alert level 1, it's the best new tool in our toolbox.
"The other thing is that if we get that very high vaccination rate, then the level of baseline restrictions will be minimal, and that's where we want to be."