Fresh modelling has highlighted the need for a "circuit-breaking" fortnight at level 4 If Auckland's daily Covid-19 case numbers track toward a disastrous health system overload.
But if transmission rates are kept low enough, a combination of high vaccination rates and level 3 restrictions could bring cases to manageable levels next month, the just-released data shows.
In their latest modelling, Te Pūnaha Matatini researchers simulated Auckland's Delta outbreak through to early January, while accounting for rising vaccine coverage by age group over time.
As at today, when another 68 cases were confirmed within Auckland, the region's full coverage had risen to 78 per cent – with 90 per cent of eligible residents now having received their first dose.
Based on local vaccination data and bookings, the modellers estimated that vaccination would have brought down the outbreak's effective reproduction (Reff) number – or the average number of cases produced from one infection – by 67 per cent by early January, compared to an unvaccinated population.
The modelling assumed that level 3 controls were held in place throughout the period they analysed, that the virus-blocking effect of the restrictions didn't weaken over time, and that contact tracers could manage 1000 active cases.
It also explored two scenarios for the future of the outbreak: one with low levels of spread, and another with rampant transmission.
In low-transmission scenarios, they found current settings could push the Reff number below 1 – it's currently considered to sit at around 1.2 or 1.3 - in November.
That would lead to case numbers likely to be manageable within the health system's existing capacity.
But in high-spread scenarios, status quo vaccination rates and restrictions wouldn't be enough to achieve that crunch – and lead to case numbers that would place "extreme demands" on the system.
For instance, median estimates from the modelling indicated that, under a scenario of "very high" transmission, weekly case numbers could reach 6629 by the week starting December 29 – with around 425 weekly hospital admissions, 378 beds occupied, and 30 deaths.
When compared with a scenario of "medium" transmission, however, those same figures for that week corresponded to 377 weekly cases, 19 hospital admissions, 25 beds occupied and two deaths.
Because of the risk that came with high transmission, the modellers looked at what difference that two weeks at level 4 early next month, followed by a return to level 3, could make to the trajectory.
They found that a fortnight spend under a harder lockdown could "significantly" reduce demand on the healthcare system, through to the beginning of 2022.
Even under a "very high" transmission scenario, they found a November circuit-breaker could result in medians of just over 1000 weekly cases by early 2022, along with 61 hospitalisations, 54 beds occupied and four deaths.
Study co-author Professor Michael Plank said the modelling, which was assessed by a rapid peer-review team, ultimately aimed to capture the combined effect of alert level restrictions and the vaccine roll-out.
"We can see that in some of our scenarios, case numbers go up, but over time they level out, and then start to come back down.
"That's what we're hoping to see, and when that comes down, that will put us in a good position to start to ease restrictions."
But the flipside, he said, was a steep case climb that led to high numbers of hospitalisations.
"That's the scenario where you'd want to look at a circuit-breaker."
Plank said it was encouraging that the number of hospital cases had fallen – 37 patients were receiving hospital care as of yesterday, compared with more than 50 last week.
"That isn't climbing much at the moment, but it could still increase – so that's a key number to keep an eye on."
Yet, asked where the outbreak was sitting in respect to the two scenarios modelled, Plank said its growing case numbers "pushes us more toward that pessimistic one".
"I'm not sure we're quite there yet, as we haven't hit the point where we're getting 150 to 200 cases a day.
"But if we do within the next week or so, I think we'd be in that scenario."
Plank noted the Government's expressed reluctance to jump back to level 4 – something Prime Minister Jacinda Ardern has contended would be unlikely to arrest case numbers because of the nature of the outbreak, and compliance.
"But I'm not sure I entirely buy that argument now. That may have been true a few weeks ago, but the outbreak has become much more geographically spread across the whole of Auckland," he said.
"So, I think a short circuit-breaker would break some of those chains of transmission and help bring case numbers down, or at least stop them from going up too steeply."
Last week, the Government unveiled a new "traffic light" system to manage Covid-19 when district health boards have 90 per cent of their eligible population vaccinated.
When each DHB hit this target, the new framework – which makes use of vaccine certificates - would come into effect.
Businesses will be able to continue to operate at each of the risk levels, and each setting can be used in a highly targeted and localised way.
Hard borders in Auckland would be retained while the virus was not widespread but once the new system is in place and the virus is widespread, Ardern didn't expect regional borders to be put in place for long periods.