New Zealand's bold call to "go hard and go early" one year ago has been further validated by new modelling suggesting Covid-19 elimination was the best option for the economy and public health.
The new Australian study has offered a glimpse at what New Zealand might have faced in 2020, had it picked trying to live with the virus over opting to wipe it out altogether with hard-line measures like lockdown.
The study simulated four different responses in the state of Victoria - which has a similar age, population and income structure to New Zealand - and then analysed how each of them performed against various health and economic indicators.
"From where I sit, this is possibly the best paper yet to try to integrate the epidemiology and economics, so we can ask what's best for society," said lead author Professor Tony Blakely, a Kiwi epidemiologist at the University of Melbourne.
The four modelled responses included "aggressive" and "moderate" elimination - both which aimed to stamp out the virus altogether, but at different paces.
Blakely described aggressive elimination as "going hard", and likened it to New Zealand's rapid, zero-tolerance approach.
Moderate elimination was more akin to New South Wales' method, which Blakely said was "not so aggressive, but getting there all the same".
The other two strategies - "tight" and "loose" suppression - effectively aimed to minimise spread while living with the virus, and had respective targets of keeping daily cases per million people to between one and five, and five and 25.
The study, published online ahead of peer review, also used two different types of models.
One was an "agent-based" model to estimate daily infection rates and the time it took to reduce them across Victoria's four-stage system, which was similar to New Zealand's.
The other model captured a wider picture, estimating long-term health impacts arising from the virus - namely health-adjusted "life years" (HALYs) - along with costs to the health system, and to GDP.
The study found that while the number of days in hard lockdown were similar across all four strategies, "aggressive" elimination came with the highest percentage of days, with the lowest level of restrictions.
It also showed the long-term health impacts of aggressive and moderation elimination were similar, and relatively low, but those for tight and loose suppression were nearly eight and 40 times higher, respectively.
In terms of virus-related deaths over a year-long period, aggressive and moderate elimination kept mortality numbers to 58 and 64 - while the two suppression approaches came with 483 and 2,249 deaths.
The total cost to the economy was estimated to be relatively similar between all strategies, but, from the perspective of health-system related costs, aggressive elimination proved the best option.
For instance, health expenditure costs for the first year came in at $3.7m for aggressive elimination - compared with $117m for loose suppression.
Blakely, formerly based at Otago University, said those results were relevant to New Zealand, which made for a "fairly good substitute" for the state.
He said while there some uncertainties and overlaps between the four modelled responses, "when you weigh it up across them, the elimination responses are optimal".
"That's probably as good as we're ever going to get to being able to understand what we should have done in 2020," he said.
"And I think it's very reassuring for both Australia and New Zealand that we pursued an elimination goal."
Blakely added that the study also captured possible unintended effects of lockdown, like anxiety and depression, but found these didn't change the overall conclusions.
University of Canterbury and Te Punaha Matatini Covid-19 modeller Professor Michael Plank agreed the results could generally apply to New Zealand.
He pointed specifically to the far fewer deaths and hospitalisations that came with elimination - and all at similar economic cost.
"This suggests when short sharp lockdowns are needed to control outbreaks, the short term pain is worth the long term gain," Plank said.
"This will continue to be the case until we reach a high level of vaccine coverage in the population."
Insights add to elimination case
The new study wasn't the first to take a retrospective look at whether elimination had proven the right choice.
Modelling by Te Punaha Matatini researchers, published last year, found that 200 Kiwis may have died had the Government held off ordering the nationwide lockdown for another three weeks - while nearly 12,000 people may have been infected.
New Zealand moved to alert level 4 on March 25, before dropping back to level 3 on April 27, during a period the country registered just over 1500 cases and 22 deaths.
Nearly 11 weeks later, Covid-19 had been eliminated.
But had the shift to alert level 4 been delayed by 20 days, the country could have recorded more than 11,500 cases and 200 deaths - and slashed the chance of eliminating the virus to just 7 per cent.
The modelling indicated that Māori and Pacific people - who have a greater infection fatality risk - could have been disproportionately affected.
The delay would have also increased the chance of a longer lockdown period being needed to bring down daily numbers to low levels, given that authorities may have still been reporting 35 fresh cases around the time alert level 4 finished.
Further modelling has underscored why New Zealand should stick with elimination.
Nevertheless, Te Punaha Matatini director Professor Shaun Hendy said many of the long-term consequences of elimination remained hard to understand - even a year on.
"Even when we look at how the economy is going to rebound, there's still a lot of uncertainty," he said.
"But the short-term impacts can definitely be justified. It's been a tough year, but we've had a better one than almost any other country you could think of."
Otago University epidemiologist Professor Michael Baker, who was instrumental in developing New Zealand's strategy, felt Victoria had also proven an important elimination model for the rest of the world.
"It's a region that has seen intense, sustained transmission - and yet has still been able to eliminate the virus," he said.
"We've heard from other advanced, Western economies that the only reason elimination worked in places like New Zealand was because they got in hard and early, and they didn't have many cases.
"That's not really correct, and Victoria provides a good case study here."
Last week, Baker and colleagues set out how a Australia and New Zealand bubble, yet to be confirmed, could be among the first of many virus-free "green zones" that would widen until Covid-19 was eradicated globally.