The Level 4 extension gives officials time to focus on finding the missing link in the chain of transmission and figuring out if the virus has been spreading outside of Auckland, Marc Daalder writes
Analysis: It really was no surprise when Jacinda Ardern said that Level 4 would be extended through Tuesday for the whole country.
There's simply been too little time to discover the full extent of the Delta outbreak. Certainly officials were in no position to be able to rule out spread outside of Auckland or take a good guess at the size of the outbreak inside of the supercity.
The four-day extension now gives contact tracers, genome scientists, lab techs and health officials time to focus on solving two crucial mysteries: How Covid-19 got from an MIQ guest into the community and whether there has been transmission in regions other than Auckland.
Even solving these unknowns might not lead to the end of Level 4 restrictions, however. Overshadowing everything is the fact that a coronavirus infection can have a long tail, showing up in some cases 14 days after infection.
"We could make [the lockdown] 10 days, but we run that risk of, if there are still people who test positive after that time, then we miss them and we've got another transmission chain. For the sake of a few days, I would be urging we treat it like a 14-day cycle," Siouxsie Wiles, a microbiologist from the University of Auckland, told Newsroom.
The missing link
The discovery of the likely origin of the cluster in a person who returned from Sydney on August 7 and tested positive in MIQ on August 9 has been extremely useful. It demonstrates that Covid-19 hasn't been circulating in the community for weeks and rules out the worst case scenario of hundreds or even thousands of undetected cases.
But it's still unclear how the virus made its way from the MIQ case to any of the known community cases. In other words, there's a missing link in the chain of transmission. As long as that link goes undetected, it raises the risk of other community clusters that we can't contact trace.
Those clusters or additional branches on the transmission chain won't be spreading the virus outside of their households now (unless they include essential workers). But we'll want to find them all before lifting restrictions, or risk them being able to spread in the future and forcing us back into lockdown again.
"If it hasn't been circulating for weeks, then we probably have got orders of magnitude [fewer] branches," Wiles said.
How large might those branches be?
Of the 31 cases in the Delta cluster right now, 19 of them are epidemiologically linked to one another. The remaining 12 are still under investigation. That means they could be linked at a later date or they could be part of those missing branches. One of them might even be the missing link.
But if we have one branch of 19 cases (with more likely to eventuate given the large number of locations of interest and how many of those locations are prone to spreading the virus to a lot of people), then we could easily have a few more the same size. Remember that each person with Delta, on average, infects five to nine others. Even if we're only missing one link in the chain of transmission, that's a potential of four to eight other branches they might have started.
Some of these branches and missing cases will turn up through community testing. Certainly in Auckland, where more than 1.5 percent of the population was tested on Thursday and another 1 percent the day before, we are likely to find most of the active community cases with time.
Once contact tracers interview these cases and line up their travel histories, they'll begin to assemble a map of infection - hopefully one which fleshes out other branches more fully.
The rest of NZ
However, cases outside of Auckland are less likely to be caught. Although Director-General of Health Ashley Bloomfield has cited a 1 percent testing threshold as a significant sample of the community, most of the country isn't hitting that mark.
Ministry of Health data on the number of tests processed between Tuesday and Thursday shows testing rates in District Health Boards outside of Auckland range from 0.2 percent of the population tested on Thursday, in the West Coast, to 0.94 percent of the population tested in Wellington.
That's likely not enough to find every case or rule out undetected branches of transmission.
This brings us to the second crucial mystery: Has there been transmission outside of Auckland?
Those tests will be part of the key to solving this one. The more people who are symptomatic get tested, the more likely officials can either rule out spread in certain areas (like the South Island) or detect and squash it.
The other part is contact tracing. There are 162 identified contacts based outside Auckland and the Waikato, though the Ministry of Health wasn't able to provide Newsroom with a breakdown of where they are. At least some are in the South Island.
This is likely to be just the tip of the iceberg. It doesn't include the thousands of people who may have been exposed at a handful of high-risk sites like schools and churches. And it's only the result of the first 72 hours of frenetic contact tracing.
In all likelihood, there are hundreds of people outside of Auckland and the Waikato who were at the locations of interest we know about. When you factor in the undetected branches and exposure sites we don't know about, that number could rise much higher.
Even people who would have been infected relatively shortly before the lockdown hit could still have spread the virus in their home communities. While Ardern and Bloomfield seemed to brush off concerns that the three Wellington cases could have been infectious prior to lockdown given they had only been infected on Sunday, Wiles said that couldn't be guaranteed.
"People can be infectious 24 hours later, right? We've had a couple of cases like that. Unfortunately, you can't rule it out," she said.
And still, overshadowing all of this is that long tail, which means contacts could test negative but develop an infection up to 14 days after they were exposed. In the end, no matter what happens over the next few days, it may all come down to a waiting game.
"I don't think we can say anything about the rest of the country not being in that [risk] zone, given that we've got a hundred odd people - and probably more - that have moved around the country. People have been going all over the place. The idea that the South Island is some magical place that isn't connected to the rest of New Zealand is a little bit ridiculous, really," Wiles said.
"It really will depend on how well they nail down all those transmission chains. Once they've got everybody in isolation, then that's when we can start more carefully coming down the alert levels. So it really depends how long that takes.
"But there are a lot of people and there are a lot of exposure times. There will be people who probably haven't come forward yet who maybe haven't been checking the lists. I think we have to be cautious and it strikes me that that's what we're going to do."
