This week's case numbers will confirm whether the Omicron outbreak is growing exponentially, experts say – but there's hope our population will be well boosted by the time it peaks.
With another 91 cases reported yesterday, experts are watching a race between the fast-spreading variant and the rollout of a booster shot that's up to 90 per cent effective at keeping people out of hospital.
Its outcome will be pivotal to how our capacity-limited health system copes when the Omicron wave peaks – potentially as early as March.
Otago University epidemiologist Professor Michael Baker was optimistic most eligible Kiwis would have received their booster before then.
"We were fortunate to be able to delay Omicron's arrival, through managing our borders."
As at today, just over 1.3 million people – that's around 30 per cent of the over-12 population, and two thirds of those currently booster-eligible – have received their booster shot, with vaccinators administering the top-up dose at a rate of tens of thousands each day.
At the same time, the child vaccine roll-out has delivered first doses to a third of children aged between 5 and 11 years.
Modellers tracking these numbers are still uncertain when Omicron will take off in the way it has among highly-vaccinated populations elsewhere – but expect we'll be able to confirm a clear trend this week.
"It's still patchy at the moment, and we only really had our first day of more than 100 cases on Friday," said Professor Michael Plank, of Te Pūnaha Matatini.
"I'd expect to see numbers doubling every two to four days, probably over the next week or two - but it's a bit early to really say that for sure."
Fellow Te Pūnaha Matatini modeller Dr Dion O'Neale also expected this week to mark a shift from the previous relatively low case numbers.
"Almost every other place in the world that's had an Omicron outbreak's seen a doubling time of around three days. We'd expect New Zealand to be similar," he told RNZ.
"So that means about 100 cases a day at the start of the week, around the middle of the week we're probably looking at around 200 cases a day, and then doubling to around 400-ish by the end of the week."
This pattern could emerge as early as Thursday or Friday, or perhaps by Sunday, he said.
Baker cited recent work out of the University of Washington-based Institute for Health Metrics and Evaluation (IHME), which explored several scenarios for New Zealand.
Each indicated a curve rising steeply from late February and peaking over March.
Under its current projections, a peak of around 2395 hospital beds would be needed by March – including around 458 in intensive care units - not long after daily cases involving some level of sickness had grown to around 11,000.
The Government has said it can surge ICU capacity to 550 beds if needed – a claim that's been challenged by clinicians.
But the IHME modelling came with several big limitations, Baker said, and also assumed an outbreak that began two weeks earlier than it actually did – meaning we could have more time to boost before the peak arrived.
Plank agreed New Zealand had a "good head start" compared with other countries that had met Omicron early in their own booster rollouts – and said whatever we could do now would matter in the long run.
"Even if we can slow things down and delay those really high case numbers by a week or two, that buys time for quite a lot of people to get boosted," he said.
"Given we're boosting something like 40,000 people a day on average, a couple of weeks of boosting will make a big difference – particularly among some of those high-risk groups."
Baker pointed out that many of those people being boosted right now were among those most vulnerable to the virus, such as older Kiwis and people with underlying conditions.
"So, I think we do have an advantage in getting reasonable booster coverage locked in prior to the outbreak wave hitting – and that will have a huge protection effect," Baker said.
"Another positive is we're learning the booster's protection against serious disease appears to be more effective that we first thought."
But he added there was still a crucial case to slash the booster's eligibility interval from four to three months, as he and colleagues have called for before.
As it stood, much of the population would become eligible only around mid-February – and it could take another fortnight after receiving the shot to rebuild antibodies.
Urgently making the booster available to more people could also help address health inequity, he said.
Not only were Māori disproportionately at risk of severe illness, the group's younger population structure meant that a large proportion currently weren't eligible.
"We know that the booster reduces your chances of getting sick and having a serious outcome, but also of passing it on to other people – so high boosting rates will really help dampen things down and flatten the curve," Baker said.
"That's why we don't want to miss the peak – because the booster rollout won't be nearly as effective if it arrives after it."