Most of the country is now at Level 3, but is that stringent enough to control a small outbreak? And what happens if we find Delta at Level 2? Marc Daalder reports
ANALYSIS: After two weeks in one of the world's strictest lockdowns, most of New Zealand is now at Level 3.
Sometimes considered little more than "Level 4 with takeaways", Level 3 actually provides a range of new freedoms. Bubbles can combine, funerals and tangihanga can proceed in a limited manner and most work can resume, except for those businesses which require close physical contact.
Of course, every added human interaction poses a risk of transmission of the virus - and Delta doubles that risk. Previous outbreaks have been successfully managed at Level 3, as with last August's Auckland cluster or the Valentine's Day cluster.
Does the same hold for Delta? If the virus managed to escape from Auckland into a Level 3 area, could it be controlled without having to move back up to Level 4?
Targeted testing and tracing
Experts are cautiously optimistic that targeted testing and tracing could manage a small outbreak.
Director-General of Health Ashley Bloomfield told Newsroom on Friday that "a case" could be controlled at Level 3.
"Our aim would be, under Level 3, if we saw a case pop up somewhere, then we could deal with that through testing, contact tracing, isolation. Recalling that Level 3 is still very restrictive on movement, and so it does provide quite a bit of cover in that situation and you can see from the Wellington group of cases, that actually, with just one or two cases there, and with the isolation and contact tracing, we’ve been able to get around that group of cases."
However, those cases have been corralled at Level 4.
Nonetheless, other experts backed Bloomfield's assessment.
"I think you could try very intense contact tracing and, if it was very well-defined, I think you could pause it for a moment," University of Otago epidemiologist Michael Baker said.
"This would be more like what we usually did in the past. You would use contact tracing to try and stamp it out, initially."
University of Canterbury mathematics professor and Te Pūnaha Matatini disease modeller Michael Plank said the context was key.
"I think potentially we could. It would depend very much on the nature of the cases. If it was a case that had a clear link to the existing outbreak who had travelled for essential purposes and the risk of onward community transmission was limited, then I think that's the sort of situation we could manage at Level 3," he said.
"The more worrying situation would be if you had a case pop up with no clear link. That would be a situation where you might move back up to Level 4."
The Level 3 restrictions are set to be reviewed on Monday. Is there a world in which most of the country is down at Level 2 while Auckland remains at Level 4?
Bloomfield said "There's no public health reason why it couldn't happen". Plank and Baker also concurred that it was possible.
The key would be managing the border between the different levels, with extremely restricted travel even for essential workers. Baker's University of Otago colleague Nick Wilson had previously called for a requirement that anyone crossing the border between Auckland and even a Level 3 zone should have to be fully vaccinated.
How Delta changes the game
There might also have to be changes to Level 2 to dampen any undetected transmission in the event of a leak from Auckland.
The alert level system was originally designed to deal with the wild-type coronavirus. While this was pretty transmissible, with each case on average infecting two to three others, it was hampered by a factor called overdispersion. In reality, many or even most cases passed the virus on to no one else, while a small percentage of cases - maybe 10 to 20 percent - was responsible for as much as 80 percent of onward transmission.
This is how some Covid-19 outbreaks in New Zealand never took off. Think of the woman who took a road trip around Northland for a week while contagious but infected no one, not even her husband who sat next to her the whole time.
Overdispersion is also responsible for the rapid explosion of the virus when enough cases are introduced to an environment. In March 2020, we had hundreds of different introductions of the virus. Most of these led to nothing, but a handful caused super-spreading events - a wedding in Bluff, a livestock conference in Queenstown or a St Patrick's Day party in Matamata - that made up a sizeable chunk of our total case count.
Delta still has the capacity for super-spreading, but it's also infectious enough that it isn't reliant on mass gatherings to spark an outbreak.
We've seen that with this outbreak, which began with just a single case and now encompasses more than 600. Almost all of the cases so far were either infected prior to lockdown or are the household contacts of people infected prior to lockdown. About half can be traced to a super-spreader event - the August 15 Māngere church service. But there are still hundreds of cases that resulted from just 11 days (at most) of community transmission prior to lockdown.
Level 3 was strong enough to control the original wild-type virus. Even without targeted testing and tracing, such an outbreak would likely diminish on its own under Level 3. But Delta is transmissible enough to continue to spread even under those restrictions. It could jump between newly-joined bubbles and run amok through workplaces that have reopened. Even if it doesn't spread to the public, it could still jump from bubble to bubble via the kitchens and factory floors of businesses operating at Level 3.
This doesn't mean Level 3 needs a major rethink in the age of Delta, but it shows why how we use it might change.
Level 2-plus?
On the other hand, Baker says, Level 2 does need to be reworked.
"Everyone basically knows that Level 2 is almost indistinguishable from Level 1, for most people. You've got restrictions on gathering size," he said.
Stopping gatherings of 100 or more people limits the potential exposure to super-spreading. But as we've seen, Delta doesn't need super-spreading to spiral into a major outbreak. And the only defence against transmission in most scenarios at Level 2 is distancing rules, which were devised before the airborne nature of some coronavirus spread was fully understood.
"Alert Level 2 is designed to get people back to work and school, which is good, but it relied on the two-metre rule or one-metre rule but that doesn't work. It's never worked against this virus well," Baker said.
He and his colleagues have been arguing since June 2020 that the alert level system needs to be reformed, adding in new levels to create a more flexible response that's updated with the latest knowledge of the virus in mind.
While it seems unlikely that the Government will make that change, they could still incorporate some of the ideas for the new levels into Level 2. The key thing here, Baker says, would be widespread masking indoors, including in schools for students above a certain age and in most if not all workplaces.
Masking could help dampen Delta transmission, such that even an outbreak that is detected late won't be as large as the one we're now dealing with in Auckland.
"We can't move down to Level 2 until it's been split into two levels. One that has mask use, universally, indoors and one that doesn't," Baker said.
"Because otherwise it doesn't pose any barrier at all to the virus."
Bloomfield told Newsroom on Tuesday that his team was looking into strengthening the Level 2 settings, including around mask use.
