A woman passes a fence outside New York's Green-Wood Cemetery adorned with tributes to victims of Covid-19 in New York. Experts doubt the US has the will to pursue NZ's elimination goal. Photo / AP
Can the world wipe out the coronavirus, as New Zealand largely has? Although scientists say eradication is unlikely, it doesn't mean we shouldn't try. Jamie Morton reports.
Last week marked a major milestone for public health.
It wasn't another battle lost to Covid-19, but a victory over a much older foe.
Having once ravaged the world, infecting millions and leaving one in every 200 cases permanently paralysed, wild polio has finally been stamped out in Africa.
Since the late 1980s, cases of the highly-contagious virus have plunged by 99.9 per cent, and the last remaining type of it hangs on only in Afghanistan and Pakistan.
Writing in the premier journal Science, researchers went as far as calling the effort - a combination of public will and an effective vaccine - the "signature success of science in the 20th century".
They naturally turned to the crisis that's before us today.
"As the world faces Covid-19, it is heartening to see the same application of science to public health for [Covid] as the one used for the past 70 years of polio-virus research."
But can eradication of the new coronavirus really be similarly achieved?
One leading Kiwi epidemiologist, Professor Tony Blakely, is optimistic.
He believes SARS-CoV-2 along with the better-known disease it causes, will vanish just like its less-virulent predecessor SARS-CoV-1, and the Spanish Flu that fuelled the last pandemic of this scale.
"Its disappearance can be hastened by a vaccine and natural immunity," Blakely said.
"It will probably take two to four years."
Other experts aren't so confident, citing, among other factors, a lack of leadership around the world and unanswered questions about immunity, vaccines and the virus' mysterious animal source.
Since its outbreak in Wuhan, China, late last year, the virus has gone on to infect more than 23 million people, and kill more than 810,000, across 216 countries, spread from Anguilla to Armenia.
Epidemiologists fear it's just getting started. One MIT projection found that by March next year - assuming no cures had been found by then - case rates could climb to nearly 250 million, and the death toll to 1.8 million.
Otago University's Professor Michael Baker has suggested as much as 40 per cent of the planet's population could become infected within the next few years.
Nations are meeting the threat differently.
Europe initially responded by locking down some 250 million people and largely cutting itself off from the rest of the world.
Borders have since re-opened to many outside states, including New Zealand, although a patchwork of restrictions remain in place as Europe pursues a suppression approach.
The United States has turned to the same playbook, using testing and a mix of state and local responses, such as stay-at-home orders and bans on large gatherings.
But, with more than 180,000 deaths so far, and criticisms over slow action, dismal leadership and a lack of testing and protective equipment, America's response has been panned as a disaster.
Sweden, which opted against lockdowns in favour of a risky gamble for herd immunity, recorded its highest death toll in 150 years over the first half of 2020.
Brazil, whose far-right leader, Jair Bolsonaro, had dismissed the virus as "little flu", and even joined anti-lockdown protests, has suffered a death toll of more than 116,000 - second only to the US.
New Zealand and its elimination strategy, on the other hand, has been held aloft as a poster child for aggressive action and evidence-informed governance.
The concept has been endorsed in the UK by its Scientific Advisory Group for Emergencies (Sage), in Ireland by top local epidemiogists such as Professor Patricia Kearney, and in Canada by prominent physician Dr Irfan Dhalla.
That's not to say there aren't better exemplars than us.
Otago University public health experts like Baker say we merely learned from Asian tiger economies such as Taiwan.
Despite being a mere 1000km from the pandemic's epicentre, the island kept Covid-19 at bay through a winning combination of tight border control and quarantine, sophisticated contact tracing methods, and a culture already accustomed to masking up.
Media outlets around the world have dotingly cast Prime Minister Jacinda Ardern as a caring, Covid-19 conqueror against an ignorant and incompetent Donald Trump.
Yet the World Health Organisation (WHO) has poured doubt over whether the Kiwi way can be applied at scale against what it called a "once-in-a-century pandemic".
In a news conference last month, WHO officials said it would be "very unlikely" that nations could eradicate the virus, pointing to the threat of super-spreader events and small outbreaks that could fast become large ones.
"It's very analogous to a forest fire," said Dr Mike Ryan, the executive director of WHO's health emergencies programme.
"A small fire is hard to see but easy to put out. A large fire is easy to see but very difficult to put out."
In a June op-ed, Dr Lee Hampton, of global vaccine alliance Gavi, pointed out that humanity had only ever eradicated one human infectious disease comparable to Covid-19 in its broad geographic distribution: smallpox.
That was down to three advantages - an effective vaccine, the ability for fast detection and the absence of an animal reservoir, which could restart transmission among humans - none of which exist to aid the world's current fight against Covid-19.
"Even if eradication of Covid-19 is ultimately technically feasible, it will likely be extremely challenging," Hampton argued.
"A strong, well-resourced effort with effective global co-operation would likely be needed for years before the disease was eradicated."
Baker felt New Zealand's approach of elimination - a label he can personally take credit for - probably wasn't appropriate for many countries right now.
"But it is appropriate for quite a high proportion of them," he said.
"In fact, while the exact pre-conditions for using this approach haven't really been defined, you can look at the countries that are pursuing it, and see that they doing it very effectively."
Coining another term, Baker called this the "Asia-Pacific approach".
There were nations like Taiwan, Vietnam and New Zealand, which had knocked down the virus through sheer control and aggression, albeit with some geographic advantages.
"Then we have exclusion, which is the approach taken by quite a few Pacific islands, where they've just lifted the drawbridge and kept the virus out."
Asked why he believed elimination could eventually be adopted globally, Baker replied: "China".
Despite its sprawling land area, and population of nearly 1.4 billion, China strangled its outbreak to the point that, by March, it was reporting fewer than 100 cases each day.
Last week, the handful of daily cases it was recording on the mainland were largely imported ones - although it had got there through vast public health resources, and an authoritarian government prepared to impose draconian measures.
"But, as China showed, I don't think it matters if you have a very established pandemic in a population," Baker said.
"If you are dedicated to elimination, you can stop a pandemic at any stage, and it would probably get easier if a country had had a virus circulating for a while, providing some level of protective immunity."
In an editorial in the New England Journal of Medicine, Baker set out the main lessons that New Zealand had for the world.
It had made a rapid, science-based risk assessment and followed that up with decisive, government action, resulting in tough controls at the border and in the community.
"You basically need three elements: you have to manage your borders, you need testing and contact tracing, and you need a very intense approach to stamp out transmission," he said.
"We often call this lockdown, but I see it more as a stay-at-home order, where people just stay inside their small bubbles for several weeks."
And although the latest flare-up has sent Aucklanders back into their homes, Baker said elimination hinged much more on the other tools in the box.
Right now, he saw the strategy as technically possible for emerging economies and high-income countries.
That was provided they had the proper infrastructure in place - New Zealand's latest outbreak has proven the value of testing, tracing and genomic sequencing - and arguably more importantly, political will.
"In even the richest country on Earth, the United States, it's hard to imagine them pursuing elimination because there isn't the political leadership. Even its infrastructure might be too stretched to deliver it."
Prominent infectious diseases expert Associate Professor Siouxsie Wiles agreed collective will was a big impediment - this had already been seen with the slow progress to fully eradicate wild polio - but so were the many unknowns still surrounding SARS-CoV-2.
Case in point was the 33-year-old Hong Kong man believed to be the world's first person re-infected with the virus, having caught a different lineage earlier in March.
Although that complicated prospects for natural immunity, virologists have reacted with little surprise, noting that other human coronaviruses - the common cold among them - can be contracted more than once.
"Mutation doesn't look like it's that big of a deal at the moment, because it is happening quite slowly," Wiles said.
"The question will be whether the vaccines that are being developed at the moment can be effective against all of the strains that are circulating.
"How do you achieve the same immune response? Do you need a vaccine that works against the spike protein from all different versions of the virus? That's really important to know."
And so was learning where the virus came from - or which particular animals, be they bats, pangolins, or something else, were acting as reservoirs.
"If there are hosts that are circulating it, that could allow it to go back into humans, then it becomes difficult," Wiles said.
"You might have to keep vaccinating new babies so there are no susceptible people in the populations."
Dr John Taylor, a molecular virologist at the University of Auckland, said if herd immunity against the virus was indeed possible, it would be difficult to achieve quickly as long as humans kept taking stringent steps to stop becoming infected.
"If we make a particularly good vaccine, we may be able to go one better than natural immunity induced by infection, by establishing a level of immunity that can suppress subsequent infections," he said.
"But even then, I think this would be an overly hopeful outcome."
A second scenario was a vaccine that might not achieve that individual "sterilising immunity", but herd immunity, with the potential to choke the virus until it died out.
A third was a vaccine that simply reduced the virus' severity.
"If the virus circulated around a population that was vaccinated, the vaccine recipients could be more likely to suffer much lower grade infections, or even sub-clinical ones," he said.
"I think that is a much more realistic prospect than just driving for the goal of elimination.
"Again, there is much we need to learn about this virus over a longer time frame. We don't know how it will mutate to a form that is able to escape immunity that becomes established from previous infections.
"And we don't know whether or not that immunity from previous infection simply fades to a level where it's unable to prevent a second infection - although it still may be able to attenuate the severity of the second infection."
The first vaccine being rolled out - Russia's Sputnik V - is claimed to deliver two year's stable immunity, and has already been given to one of President Vladimir Putin's adult daughters.
Experts here and around the world have responded with heavy scepticism.
"Ultimately, we can't say how long immunity to this virus can last, because we've only known about it for less than a year," said Professor Mick Roberts, an infectious diseases modeller at Massey University.
"We can't even say whether we'll get immunity, because no one has ever tested that. Does Putin have a crystal ball?"
Baker, too, acknowledged scientists had much to understand about our immune response to the virus - and particularly what immunity might have already been built up after months of global circulation.
"There may also be cell-mediated immunity, which doesn't involve antibodies, and is harder to measure," he said.
"So I think there are still quite a few surprises in store for us when it comes to how this virus behaves at a population level."
At a global level, Baker figured total eradication would be a tough ask without a vaccine.
When an agent did arrive, he said, programmes could first target high-priority groups, like front-line health care workers, and even younger people, who were more socially connected and thus more likely to spread the virus.
"Where does elimination fit in here? I think this is something countries could try to do while they are waiting for the vaccine," he said.
"It's better for population health and it's better for the economy. So, while I tend to agree with others that the real exit strategy for the whole world is a vaccine, elimination is how you can protect your population until that arrives."
Can the world really repeat its triumph against wild polio?
Ultimately, the next crucial few years will prove whether mankind's response to Covid-19 becomes the "signature success of science" of this century.
