COVID-19 modeller says moving Auckland to level 3 and rest of country to level 1 could've caused 'explosive outbreak'

A top COVID-19 modeller says keeping Auckland at alert level 4 and the rest of New Zealand at level 2 was the right call, protecting us from a resurgence that could trigger an "explosive outbreak".

Professor Michael Plank, of Te Pūnaha Matatini and the University of Canterbury, says Cabinet was correct to take a cautious approach, as recent mystery cases indicate there may be undetected community transmission in Auckland.

And while he acknowledges large swathes of the country will be frustrated to remain at alert level 2 when there are no known cases, he points out there are thousands of people crossing the boundary each day.

"No border is watertight and so while there are active community cases in Auckland, alert level 2 is an essential safeguard if a case does leak out," Prof Plank told the Science Media Centre.

"A move to alert level 1 would risk another explosive outbreak in another part of New Zealand, which would send the whole country back to square one."

It's not just those outside Auckland who may be frustrated by the Government's cautious approach to alert levels - it's those in the region too who, until the mystery cases emerged, might have been expecting to be moving down.

But Prof Plank says if Auckland moved to level 3, that too could "trigger a resurgence" of COVID-19 that would "set us back weeks".

"Model results show that it could [take] up to two weeks for us to see the effect of this resurgence in our case numbers, by which time the number of people infected could be much larger."

On Monday, Prime Minister Jacinda Ardern announced an in-principle decision to move Auckland to level 3 in eight days' time.

Prof Plank says this shows public health teams are confident the Delta outbreak is coming under control.

"Provided the number of unlinked cases and cases infectious in the community both trend downwards over the week ahead, [level 3] is a realistic possibility," he said.

"A crucial factor in building confidence the outbreak is contained over the next week is community testing. It's absolutely essential that anyone with any symptoms get tested immediately.

"Don't wait to see if it gets better. Don't think it can't be COVID because you've been vaccinated. Don't chalk it down to a cold. Colds have actually become less widespread in the last few weeks due to the lockdown. So, if you do feel unwell, it could very easily be COVID."