New Zealand could be dealing with hundreds of daily Covid-19 case numbers for months if an easing of Auckland restrictions pushes the outbreak's peak back into 2022, a modeller says.
The Government is set to loosen Auckland's 11-week lockdown with a shift next week to "level 3.2" - enabling retail outlets and public facilities to re-open, and groups of up to 25 to meet outside - despite rising case numbers in the city.
Te Pūnaha Matatini modeller Professor Shaun Hendy said case totals were continuing to rise exponentially, even with Auckland's first-dose vaccination rates climbing above 90 per cent.
Experts had hoped that, as the effect of mass vaccination increased, the outbreak's effective reproduction number – or the average number of cases produced from one infection - would soon be pushed below one, making the outbreak more manageable.
"But that's not happening, because, while we're getting gains from vaccination, we're loosening up restrictions at the same time."
Yesterday, Director-General of Health Dr Ashley Bloomfield presented modelling projections that showed case numbers peaking at between 200 and 300 per day some time in the next four to six weeks.
Hendy said cases peaking at those levels in coming weeks, before beginning to drop ahead of Christmas, could be expected in a scenario where status quo restrictions stayed in place.
"The concern is that, if we do shift to 3.2, and then 3.3 presumably a few weeks after that, then we might not see the peak for months," he said.
"We may still be dealing with an outbreak that has maybe 300 cases a day for a number of months."
There was also a risk of the virus spreading into other parts of the country - particularly those places with low vaccination coverage - over the holiday period.
Last month, Te Pūnaha Matatini released modelling indicating that, under a "high" transmission scenario - close to trends being observed now - weekly case numbers could have reached more than 2000 by the first week of 2022.
When they simulated a circuit-breaking, two-week stint at level 4 in early November, those same numbers dropped to just over 1000 weekly cases.
Hendy remained of the view that a jump back to level 4 - a prospect apparently now unlikely - could buy the health system time until vaccination was doing "the heavy lifting for us".
"At the moment, instead of allowing vaccination to really start bending the curve, we're basically using it to relax restrictions," he said.
"That means the curves are staying on the same trajectory, and that vaccination is not having the same impact that it could."
Prime Minister Jacinda Ardern has repeatedly contended an alert level hike would be unlikely to arrest case numbers because of the nature of the outbreak, and compliance.
Hendy however said the outbreak no longer appeared to be mainly driven by household-to-household contact in one part of the city, but by a mix of factors spread across the region, such as schools and more workplaces re-opening.
"It's now a lot more extensive across Auckland, which does point to those loosened restrictions playing a role."
It was critical that levels remained low enough for contact tracing to continue making a difference - but that threshold could be fast approaching.
On October 15, Ministry of Health director of public health Dr Caroline McElnay said contact tracing services would be overwhelmed at around 160 or 170 daily cases.
Hendy's fellow Te Pūnaha Matatini modeller Professor Michael Plank expected that, if case numbers did soar to levels that pushed the health system toward overload, then tougher restrictions would need to be considered.
"I think we'd have no other choice but to take action to stop it."
Earlier, the outbreak was growing at a rate where numbers were doubling around every 10 to 14 days.
While numbers were clearly still rising, Plank said that the period of time in which they doubled had since appeared to have lengthened.
An optimistic scenario still remained that the outbreak peaked before 2022, he said, and case numbers then began flattening out.
"But, counteracting that is the fact that senior students went back to school last week, and now we've got this move to level 3 step two," he said.
"The hope is that a combination of increasing vaccination rates and restrictions does keep cases at a manageable level - but it's a very delicate balancing act.
"If our contact tracing system struggles to cope with demand that could mean cases accelerate. The planned move to step 2 next week may need to be revisited if there are signs this is happening."