Covid 19 Delta outbreak: Why Auckland could move to level 3 next week, and what to watch for

ANALYSIS

Aucklanders could move out of level 4 in a week if they continue to tread the path they have so far.

Modelling released by Te Pūnaha Matatini suggests the R value has dropped to 0.4, and while cases might still be popping up at the start of next week, infections in the community may have dropped to zero.

"We do see that in some simulations," says Covid-19 modeller Professor Shaun Hendy.

"It's probably a little bit longer, on average, before we get into that position, but it's still possible that the Monday decision [by Cabinet] could be for Auckland to go to level 3."

The biggest threat to prolonging level 4 is any transmission outside of people's bubbles.

The best indicators of that likelihood are the number of mystery cases, and cases that were infectious in the community.

The latter are the ones we know about who, for instance, have been going to the supermarket or an essential workplace. These have been steadily declining; there were 27 such cases a week ago, five on Sunday, and four on Monday.

The number of mystery cases suggest missing links in the infection chain, who could also be out and about.

There were 58 such cases two Sundays ago. Yesterday there were 24, 19 of them in the past fortnight, and 10 in the past week.

Some of them are likely to be linked eventually. The Middlemore Hospital patient, for example, is one of eight people with the virus in a household of 11, and director-general of health Ashley Bloomfield is confident a link to the outbreak will be found.

Another factor is whether any of them are essential workers. An exposure event at an indoor, poorly-ventilated workplace for eight hours is clearly riskier than one at a supermarket for 20 minutes.

At last count there were only four workplaces where transmission is thought to have occurred, and none in the past week.

Professor Shaun Hendy says the signs point towards eliminating Delta, but it's so infectious that a case outside of isolation could easily see the outbreak flare up again. Photo / Supplied

Bloomfield has said that the number of cases doesn't have to drop to zero for restrictions to be eased. Those already in isolation are not a concern.

But the number of cases infectious in the community - including undetected ones linked to mystery cases - will likely need to fall to zero or near-zero before Auckland can farewell level 4.

Near-zero allows for the odd mystery case where public health officials are confident a link will be found.

A few days of such cases flatlining would provide more confidence because, as Professor Michael Baker explains, there's a lag time, and today's numbers reflect events from four or five days ago.

"You want to see a sustained period of no new cases in the community which are unexplained," says Baker.

This was essentially the path out of level 4 for the country south of Auckland. When Cabinet signalled a move to level 3, there had been several days without cases outside Auckland that weren't already in isolation.

The cases that continued to pop up in Wellington were all known contacts and already isolating.

When Cabinet agreed to move non-Aucklanders to Delta level 2, there had been no signs of any cases infectious in the community for at least two weeks, a full incubation cycle.

Some uncertainty remained around the 5000-plus contacts who were yet to be reached.

But that will be much less of a factor by Monday - when Cabinet will review alert levels - because the number of contacts has plateaued, and only one of the 1000-odd very close contacts remains elusive.

Ardern will be mindful of the danger of moving out of lockdown too quickly.

Level 3 might feel similar to level 4 for many, but it opens up a lot more chances for the virus to jump between bubbles.

That's because bubbles are bigger, allowing for caregivers, the workforce expands to include contactless services, and gatherings up to 10 are allowed to funerals and weddings.

Alert level decisions are also about more than the nature of new cases.

Other factors include wastewater testing results, and high community testing - 7000 in Auckland per day - to give public health officials confidence that remaining cases are being found.

There's obviously a lot that can happen in the next week that could wrestle Auckland towards more time in level 4.

Not all of it is in Aucklanders' control. There might be undetected cases who are asymptomatic and unwittingly venturing out into the community.

But there is plenty that can be done - and Aucklanders have been doing it well.

If they sustain for a bit longer, the freedoms of level 3 and then Delta level 2 may not be too far off.