In March, the first major wave of COVID-19 was hitting hospitals in Australia and New Zealand. Up until then, the two nations had been largely in lockstep as they struggled to flatten a climbing curve of caseloads. But, by the end of the month, they would splinter down very different paths.

Australia stuck with the original plan: rolling out tougher restrictions on gatherings and movement to suppress the spread of the virus from person to person without grinding the nation (and the economy) to a complete halt.

“It’s what we do for pandemic influenza, the same dog-eared plan countries around the world have been clinging to since this started,” says the doctor who devised New Zealand’s COVID-19 response, Professor Michael Baker. “We assume it’s already unstoppable and it becomes about controlling the impact. It’s a good plan – except it’s for the wrong virus."

So New Zealand did something he admits was “a wee bit radical”.

Instead of following most of the West into short, staged shutdowns, Baker convinced Prime Minister Jacinda Ardern to follow China, where the outbreak began, and roll out a hard and immediate lockdown with the aim of eliminating the virus altogether. It was a risky gamble. Twenty years before, one such “go hard, go early” strategy had helped Asia stamp out the first deadly coronavirus of the modern era, SARS, but could it work against a virus both more contagious and harder to detect?

By June, New Zealand got its answer. It announced it had eliminated COVID-19 locally. A difficult victory to hold onto during a pandemic. But, after almost seven weeks of tough stay at home orders, Kiwis now enjoy freedoms Australia is unlikely to see nationwide for some time.

“We’re already back at nightclubs and sports stadiums,” Baker says. “We can hug and kiss. Apart from our [international] borders and staying vigilant [with testing and surveillance], it’s back to life as usual. And it’s not too late for Australia to join the club.”

A growing chorus of Australian experts now say Melbourne’s second major outbreak – and second shutdown – is the perfect opportunity to roll out a harder, NZ-style lockdown at reduced cost and so take a shot at elimination ourselves. The Victorian government has not ruled out bringing in tougher “stage four” restrictions as it battles record caseloads (Chief Medical Officer, Brett Sutton, has even flirted with the ‘e’ word as “worthy of consideration”) but the federal government has warned elimination is impossible – and trying for it could be dangerous while the pandemic still rages globally.

Could Australia actually eliminate the virus? How tough would restrictions have to be? And would it be as economy-destroying as our Prime Minister fears?

Suppression, elimination, eradication – what’s the difference?

The strategies of suppression and elimination both use the same tactics (such as contact tracing and bans on gatherings), so the difference is largely about timing and intensity. Suppression means bringing in interventions until new cases have fallen to “acceptable levels” (at the very least within the capacity of the healthcare system). It’s what Stephen Duckett at the Grattan Institute sometimes calls the Goldilocks approach to pandemics, a delicate balancing act of restrictions that must be tight enough to keep community spread low but not so tight so as to inflict devastating economic harm for too long.

Meanwhile, under an elimination strategy, the toughest measures are brought in early and kept in place until there are zero new infections caught locally.

New Zealand and Australia rolled out nationwide stay at home orders in the same week of March. Australia's Prime Minister Scott Morrison had narrowly pulled back NSW, Victoria and the ACT from pursuing a stricter lockdown where just essential services such as pharmacies, supermarkets and petrol stations remained open. But New Zealand pushed ahead with the tougher measures. There were no haircuts or takeaway coffees across the ditch, schools and universities closed, and essential workers – those allowed to leave their home for work – fell to less than 15 per cent of the population.

Within a month, Australian states began to wind back their rules. Kiwis stayed home for almost seven weeks, but Baker says it took more testing and searching for the virus "and disbelief to be finding no trace" before New Zealand fully reopened domestically in June.

Defeating a virus locally doesn't mean it's gone for good. Measles is now considered eliminated in Australia, for example, but because the disease still pops up so often overseas, it is not yet near eradication – or global extinction.

While some illnesses (including polio) are coming close, only smallpox has been wiped off the face of the Earth, officially. A disease as contagious as COVID-19 is unlikely to disappear any time soon. Even with a vaccine, experts expect we will see dangerous flare-ups for some time yet.

Still, those in the elimination camp argue that once the virus is gone from the community, the risk of new outbreaks can be managed down to very low odds through strict border quarantine and ongoing surveillance testing. But if some virus is left to circulate under suppression, outbreaks become inevitable, Duckett says – spot fires on which we must dump stricter public health measures such as localised lockdowns or “ring-fencing” until they are stamped out. In some cases, as we have seen in Melbourne and elsewhere overseas, entire cities will have to shut down from time to time to stop cases spiralling again.

“It traps us in this stop-start, yo-yoing of the economy until we get a vaccine,” Duckett says.

What about suppression but where we really mean business?

Australia’s Deputy Chief Medical Officer, Nick Coatsworth, has injected yet another term into the debate to describe the nation's current approach. “Aggressive suppression” is the kind that could lead to elimination by happy accident because outbreaks are hacked back again and again through a rapid-fire system of testing, tracing and quarantine. While the public health response so far has not always been perfect, this approach has already seen elimination (more or less) achieved in most Australian states and territories, with long weeks passing without locally-caught cases. Even NSW, once the centre of our first wave, came within a whisker of elimination itself, having stamped out virtually all community transmission for weeks until the latest Victorian outbreak spilt across the border.

But this time, there is a key and dangerous difference. The main hotspots for the virus are no longer the hotels and households of those returning (already infected) from overseas. It’s the Victorian community itself. That means COVID-19 has now gained a foothold in the state. Cases are harder to find and so harder to contain before they infect others.

If we’re going to take a shot at elimination, epidemiologist Tony Blakely says, we need to move fast before the window closes.

But is elimination actually possible in Australia?

Baker is aware most countries could not do what his own did. For starters, New Zealand is a small island nation, able to seal off its borders, and relatively wealthy, so able to bear the huge economic hit upfront. But other countries with bigger populations, such as Vietnam and Taiwan, have also stamped out local spread. China smashed its own curve even in the very centre of the original outbreak, Wuhan, where it was once recording new daily cases by the thousands.

"There's no guarantees but elimination's been shown to be biologically possible for this virus," Baker says. And if anyone could join the elimination club it's Australia.“I’m surprised the government would have any doubts now we’ve seen it done in [parts of] Asia."

Moving fast is important. When New Zealand locked down on March 26, it had just over 200 cases and no deaths. Taiwan, China, Vietnam and other success stories also tried for elimination early. But Duckett and Baker both stress Australia has not missed the boat.

“People looked at China and thought, well that’s China, we couldn’t do that here [in a democracy],” Duckett says. “But then New Zealand did it too and that was embarrassing.”

Still, those in the suppression camp, including Prime Minister Scott Morrison, say elimination is impossible while the pandemic still rages globally. Any victory would be uncertain at best, and come at too high a cost, both to the economy and the welfare of those living under lockdown.

No country can completely seal itself away, NSW Premier Gladys Berejiklian has warned. Our guard will slip somewhere. As the story of Victoria’s resurgence shows, it only takes one or two cases to ignite a whole new outbreak.

Australia could have eliminated the virus before this latest surge hit, Coatsworth notes, and it still would have gotten loose again in Victoria. But had the rules been relaxed all the way, and physical distancing already out of fashion (in a NZ-style domestic reopening), it likely would have been even more disastrous. Therein lies the danger of pursuing elimination, the federal government argues.

Asked how New Zealand is guarding against such complacency, Baker says surveillance testing is still continuing, although not quite at the levels seen during the lockdown.

“We’ve had a couple of scares with quarantine ourselves, and I think Victoria has given us a bit of a wake-up call too,” he says. “Maybe we were becoming too complacent. We’re pushing now for everyone to own a mask in case we have to respond to an outbreak. But we’re still in a much better position living without the virus than struggling along with it.”

What would it take to eliminate COVID-19 in Australia?

Given community spread of the virus has already been stamped out in most states, many experts expect a hard lockdown would be needed only in Victoria, and possibly NSW.

If Melbourne were to follow the NZ model – and tighten its existing shutdown to so-called stage-four restrictions where schools close and only essential services stay open – then Blakely and his colleagues at the University of Melbourne calculate it would have about a 50-50 shot of wiping out the virus within the six-week shutdown window. Victoria has already moved to impose mandatory mask-wearing for those over the age of 12 from July 23, which also pushes up the odds of elimination.

“But the situation in Victoria’s been getting more out of control every day,” Blakely says. “We’d probably have to lock down a bit longer than the six weeks to do it now. Still, it wouldn’t come at a great extra cost, we’re already shutting down. It’s ballsy, I get that, but why not try?"

Duckett agrees that Australians who are weary of restrictions shifting beneath their feet could be united behind a clear goal of elimination. (“An extra two weeks now might save us another six again in the future.”)

Such a strategy would need its own off-ramp too, Blakely says. If it wasn't working, experts could then pivot back to suppression. The Australian Medical Association, which is also calling for stage-four restrictions in Melbourne, argues that if elimination is the wrong move, it can be quickly reversed.

Of course NSW, itself “now teetering on the edge” of danger, would also have to be on board, Blakely says. “There’s no way Victoria could keep out [the virus] if NSW refused to try too. But the NSW Premier [Gladys Berejiklian] is in the suppression camp."

Then there are the federal politics. In New Zealand, Baker and his colleagues at first faced resistance to their elimination plan. Some blasted the move as an overreaction (“using a sledgehammer to kill a flea”). But Baker says business leaders soon fell into step with scientists in calling for the approach as “the better plan, long-term”.

Others point out NZ may have had fewer options. Its healthcare system was not in any shape to handle the coming surge of cases and its existing contact tracing teams were “woefully resourced”, Baker admits. A lockdown bought the nation critical time to ramp up its response capacity. And there was Ardern herself, already riding high on a wave of popular support, who proved to be a powerful communicator for the road ahead, posting regular lockdown "check-in" videos over Facebook.

Getting such a plan through Australia’s own “COVID policy wars” is another matter, Duckett says. "We're more divided here. It's about political will. If you go for elimination that’s a measurable target against which a government can fail."

But what about the economy? Isn’t this over the top?

Prime Minister Scott Morrison warns elimination would spell doom for the economy, and effectively seal off imports, shipping, even people returning to Australia. “You're talking about hundreds of thousands of more people unemployed for a start,” he has said. "You can't mortgage off your economy for what would prove to be an illusory goal ... That is the [advice] I have."

Victoria's current six-week lockdown alone is estimated to cost the national economy $3 billion.

But Duckett, a health economist and the former head of the Commonwealth health department, says the economy is already on pause under a suppression strategy – elimination would not necessarily need anything more drastic at the borders beyond hotel "quarantine [for returning Australians] that actually works".

Analysis by researchers at the Massachusetts Institute of Technology (MIT) suggests US cities that locked down early and for longer periods during the 1918 Spanish flu pandemic, for example, had fewer deaths and healthier economies when it was over, as local industries were able to bounce back faster. Long-term, Duckett expects the costs of eliminating COVID-19 in Australia will be less too.

New Zealand's Baker agrees that suppression might prove to be the “worst of both worlds”. “You’ll keep getting outbreaks, it’ll keep getting into healthcare and aged care and killing lots of people, and then there’s the cost of shutting down and starting up all the time. Some businesses can’t operate in that kind of economic limbo.”

Still other experts have also echoed the government's concern that lockdowns would have to run too long and too hard to have a chance of working - and then could fail anyway. While Professor Sutton in Victoria has said elimination shouldn't be off the table, he notes a lockdown that worked in one country might not work in Melbourne - especially now community transmission has taken hold.

But if Australia doesn’t join the elimination club, Baker says it could also risk being isolated in the region as New Zealand considers forging travel bubbles with COVID-free countries such as the Pacific Islands and parts of Asia.

Blakely admits he’s worried about Victoria, and possibly now NSW, becoming pariahs just in their own homeland. “Elimination is painful, I get that, but how can Australia’s economy restart properly if we still have one state or two states cut off?

“Queensland’s already stolen the AFL!”