A year and a half since the first Covid-19 cases were identified, many countries in Asia-Pacific feel right back where they started.

While Britons hit the nightclubs after a long winter of coronavirus restrictions, millions of people in Australia and China are back in lockdown. Health systems in Malaysia, Thailand and Indonesia are overwhelmed. And countries like the Pacific island nation of Fiji, which last year had only reported a handful of cases, are now battling major outbreaks.

To some, it's hard to understand why Asia-Pacific is being hit so hard. Many Asia-Pacific countries turned themselves into hermit nations, closing off borders to almost all foreigners, imposing strict quarantines for arrivals, and introducing aggressive testing and tracing policies to catch any cases that slipped through their defenses. They lived with these tough border rules so cases could be brought down to zero -- and keep people safe.

And it worked -- until the highly contagious Delta variant took hold.

Now the fresh outbreaks are throwing the zero Covid strategy favored by China and Australia into question, and prompting a larger debate about just how sustainable the approach is.

A quiet street in Melbourne during the city's sixth lockdown on August 6, 2021.

In Australia's Covid hotspot New South Wales -- the state that's home to Sydney -- authorities have said reaching a 50% vaccination rate could be enough to start easing the state's strict lockdown, a shift from the country's previous attempts to bring cases down to zero.
In China, where a handful of cases can prompt mass testing, a growing number of public health experts are now favoring a mitigation, rather than zero-tolerance, approach, according to Huang Yanzhong, senior fellow for global health at the Council on Foreign Relations.
The shift away from the zero Covid approach is one that other fortress territories like New Zealand and Hong Kong will likely have to make eventually, experts say -- they can't stay shut off from the world forever. Hong Kong has confirmed about 12,000 cases since the start of the pandemic, while New Zealand has confirmed just over 2,880 cases -- and neither currently have any confirmed local cases, according to their respective authorities.
"The zero Covid strategy obviously has been successful in some parts of the world over the last 18 months. I don't think anyone wants it to be the future," said Karen A. Grépin, an associate professor at the University of Hong Kong's School of Public Health. "The choice now is: when do you want to start letting people die? It won't be a perfect transition, there will be parts of the population that will get this and will die."
Did China and Australia take the right approach?
While Covid-19 was rampant in Europe and the US, countries like China and Australia took an elimination approach -- they wanted zero local Covid-19 cases.
There was some cost involved. Tourism-dependent countries like New Zealand and the Pacific islands, for instance, saw their travel industries take a huge hit. Thousands of Australians couldn't come back due to limited flights and quarantine spaces -- and Australians couldn't go overseas without an exit visa.
But there was also a huge benefit. China and Australia never saw the same catastrophic outbreaks that hit the US and the UK. And up until a few weeks ago, life was largely back to normal, with people gathering for music festivals and sports events.
"The Asia-Pacific countries, by and large, have had an incredibly successful year and a half responding to Covid," Grépin said. "It would be very difficult to say that the strategies adopted in this region were not good ones."

Singer Tina Arena at the end of the first concert of her National Enchanté Tour on May 2, 2021, in Brisbane, Australia.

Dale Fisher, a professor in infectious diseases at Singapore's National University Hospital, said Australia and China's strategies were focused on tight border closures -- and quickly tracking any cases that leaked through with mass testing. But those approaches have been sorely challenged by Delta, which is estimated to be as transmissible as chickenpox, and is between 60% and 200% more contagious than the original strain first identified in Wuhan.
"I believe that (China and Australia) overrated the integrity of their borders," Fisher said. "It just may not have been such a big problem with the Wuhan version. But then you get something much more transmissible, and then any breach is exposed."
Once Delta arrived in Australia, it exposed a major flaw in the country's strategy -- a slow vaccine rollout. When other countries frantically rolled out vaccines earlier this year, Australia's leader seemed to be in no rush.
"We ... have a front-row seat on the roll out of the vaccine in many other countries where they have had to (roll them out) because of their urgent crisis situation," Australia's Prime Minister Scott Morrison said in March. "And the learnings from that have been taken into account."

As of Sunday, just 17% of Australia's population of 25 million people have been fully vaccinated -- well below the UK's 58% or 50% in the US -- meaning there is little immunity in the community to stop Delta's spread.
"(That) was a huge mistake," said Alexandra Martiniuk, a professor at the University of Sydney school of public health. "So we are stuck in this position (in Australia) where there's very few people vaccinated and a very dangerous variant."
Can a zero Covid approach work?
Chinese authorities have clamped down on domestic transport and rolled out mass testing after more than 300 cases were detected in more than two dozen cities across the country. They're familiar strategies in China -- and they will probably work again, said Ben Cowling, a professor of infectious disease epidemiology at Hong Kong University.
"For this outbreak, I think they'll be down to zero fairly soon, but it does illustrate the risks of Covid still in a zero Covid strategy," Cowling said. "This won't be the last outbreak -- there will be more outbreaks in the months to come."
For months, the zero Covid strategy has worked well. While other countries have battled overburdened health care systems and high numbers of deaths, China and Australia have reported just 4,848 and 939 deaths respectively. That's allowed them to resume life as normal within their borders, and meant their economies have taken less of a hit.

Longer term, though, many experts think a zero Covid strategy isn't sustainable. Eventually, all countries will want to open up to the world again -- and when they do, they may need to accept that some people would likely get ill, a hard shift in Asia-Pacific countries used to keeping the virus out altogether.
"Unless you're prepared to cut yourself off from society forever, you're going to have Covid in your country. So it's a question of when you let it in, and when you live with it," Fisher said.
That shift could be tough politically.
In China, for instance, officials and state media have praised the country's strategy and its success as a sign of Chinese superiority, said Huang, from the Council on Foreign Relations. The government would need to justify its decision if it moves from a zero Covid to a mitigation approach, he said.
"This containment-based approach is still popular among the Chinese populous, in a way that's a reflection (of) how this has been so internalized among the Chinese people. They accepted it as the only effective approach in coping with the pandemic," he said. "So we're not talking not just about the shift of the incentive structure of the government officials, but also to change the mindset of the people, to prepare them for a new strategy."

Police, security guards and volunteers help enforce a cordon around a neighborhood placed under lockdown after a resident tested positive for Covid-19, in Shanghai, China, on August 3, 2021.

But ditching the zero Covid strategy isn't something Australia and China should necessarily be thinking about right now, said Grépin.
When more than 80% of people are vaccinated, countries can loosen borders, Fisher said.
China relies on homegrown vaccines, including Sinovac, which had about 50% efficacy against symptomatic Covid-19, and 100% effectiveness against severe disease, according to trial data submitted to the WHO, and Sinopharm, which has an estimated efficacy for both symptomatic and hospitalized disease of 79%, according to the WHO. That's lower than both Pfizer/BioNTech and Moderna's vaccines, which are more than 90% effective against symptomatic Covid-19.
In China, they may need to add additional shots to increase immunity, Grépin said.
Opening borders too early could mean "the death that they fought so hard to avoid will happen," she added.
It's not over
The collective experience of China and Australia also highlights the risk that other countries with tough border restrictions might not be able to keep out Delta -- or another variant -- forever.
Fisher said Delta outbreaks would likely happen in other countries that had so far not experienced it, such as New Zealand.

An abandoned luggage trolley in front of the Jetstar terminal at Auckland Airport domestic terminal on October 7, 2020, two days before the lifting of restrictions for the Auckland region that were put in place following the re-emergence of Covid-19 in the community.

Like Australia, New Zealand and Hong Kong have comparatively low vaccination rates with 16% and 39% respectively fully vaccinated, as of Sunday. If Delta gets in, they are also vulnerable to outbreaks.
"There should be the same urgency to vaccinate when you don't have Covid because it's just a matter of time, and we know the social and economic impact when you have to lock down and mass test as a response," Fisher said.
He recommended maintaining some restrictions -- like wearing masks indoors -- even when a country had sealed off borders, and no local cases were reported.
"Every country should pretend there's cases in their borders, and at least have mask wearing indoors, limit gatherings," he said. "Sure that bothers people, but I can tell you, when you get a case, suddenly life's a lot easier."
Countries needed to keep learning from other countries about how to handle the pandemic, Fisher added.
"If anyone thinks this is over, they're wrong," Fisher said, "Everyone's got to face up to it and live with it someday -- and it's not over for any country yet."