SYDNEY/BEIJING/HONG KONG - When a single Covid-19 case suddenly emerged in New Zealand last week, the country adopted the approach it has used repeatedly since the pandemic began: It went into a strict lockdown to try to crush the virus.
Earning bemused global headlines for ordering a lockdown due to just one infection, Prime Minister Jacinda Ardern said the government had seen the benefits of swiftly imposing lockdowns, which had kept the country free of Covid-19 for the previous 170 days.
"Going hard and early has worked for us before," she told reporters.
Yet, the country is fast learning that the Delta strain is, as Ms Ardern admitted, a "game-changer".
Since the first case emerged early last week, the outbreak has expanded to 210 cases. On Wednesday (Aug 25), the country recorded 62 new cases.
The worsening outbreak is presenting New Zealand with the challenge that has been confronting other nations around the world that have been pursuing an elimination strategy.
As the Delta strain takes hold, it is no longer clear whether previous approaches - a mix of lockdowns, quarantine, mass testing and swift contact tracing - can suppress the virus.
The authorities in countries such as China and Australia are now grappling with whether to continue to strive for zero cases, or to prepare to live with Covid-19.
In Australia, this dilemma has split the nation.
The state of New South Wales, which is in the grip of a worsening outbreak, has recently abandoned its elimination strategy, while others, such as Western Australia, are determined to keep cases at zero.
Health experts are also divided, though all agree that speeding up vaccination roll-outs is the most effective way to deal with the Delta strain, particularly if state and federal authorities want to eventually open their borders.
An infectious diseases expert, Dr Paul Griffin, an associate professor at the University of Queensland, said on Wednesday that states such as Queensland will inevitably face outbreaks due to quarantine or border breaches.
"There is so much Covid-19 around it is unrealistic for us to expect to keep it out altogether," he told the Channel Nine broadcast network.
"We have excellent rates of testing and we need to keep that up, and the use of masks is great. But... getting as many people vaccinated, that is the key."
In contrast, China has signalled that it will not be deviating from its "zero-tolerance" approach, despite a recent outbreak of the Delta variant.
Its recent cases began at an airport in Nanjing on July 20, and saw the Chinese authorities turn to their well-worn playbook of mass testing, quarantines and movement curbs.
At one point Beijing was sealed off to places with Covid-19 cases, with trains, flights and long-distance buses cancelled. Those travelling into the Chinese capital had to present a negative nucleic acid test.
But the draconian measures were effective and China logged zero domestic infections on Aug 22.
The Chinese authorities have signalled that they would continue to stick with their current approach, though vaccinations will continue to be a big part of the country's strategy.
Chinese epidemiologist Zhong Nanshan said last week that China would need to vaccinate more than 80 per cent of its population to establish herd immunity, and that this milestone could be reached by the end of this year.
"Therefore, the current strategy is not to focus on treating cases. The most important thing is to cut off the spread of cases. This is a very important guiding ideology," he said.
Similarly, Hong Kong is seeking to achieve "zero infection" and has adopted one of the strictest quarantine and border control measures in the world in order to resume cross-border travel with the mainland.
The strategy seems to have worked, with the city recording only two local infections this month and none in July.
But cross-border travel with the mainland remains hampered as the pandemic flares up from time to time in the territory or the mainland.
Amid this, the Hong Kong government last week backpedalled on a decision to shorten quarantine periods to seven days for vaccinated travellers from medium-risk places like Singapore and Japan.
It also bumped up more countries like the United States, France and Malaysia to the high-risk category, while Australia was moved to medium risk from low risk.
On Tuesday, Chief Executive Carrie Lam said the debate on pursuing a zero infection strategy "is not a black and white issue".
Taking the example of Singapore, she noted that its vaccination rate is about 80 per cent of the population, while the figure is less than 60 per cent in Hong Kong.
"So there is a huge difference between the vaccination situation in the two places. That is, perhaps, one factor that (the) Singapore Government has taken into account, whereas I have to take into account that we have not reached a reassuring rate of vaccination in the population," she said.
Epidemiologist Ben Cowling, a professor at the University of Hong Kong, thinks the target of zero infections has been "the optimal strategy for Hong Kong in the past 18 months".
"But there are considerable social and economic costs of a zero Covid-19 strategy, and it may be difficult to justify in the longer term," he said.
"Public health measures were fully justified to buy time until vaccines were available. Now, with vaccines widely available for anyone 12 and older, I think we should plan a timeline to relax the public health measures in a stepwise manner based on higher and higher levels of vaccine uptake."
Expressing a similar view, Australia's Prime Minister, Mr Scott Morrison, said this week that any attempt by New Zealand or other countries to remain at zero cases in the long term was "absurd".
"Any state and territory that thinks that somehow they can protect themselves from Covid-19 with the Delta strain forever, that's just absurd," he said. "The way through is to get to those 70 and 80 per cent (vaccination rates), open safely."
Asked about these comments, New Zealand's Covid-19 Response Minister, Mr Chris Hipkins, said on Wednesday that it was "too early to throw in the towel now".
"We do want to see a time when lockdowns are not the answer to cases in the community," he said. "But we are not there yet."