By Julia Hollingsworth, CNN

Covid-19 cases are rising in countries praised for stopping outbreaks. Do they need to change their strategies?

Updated 5:00 AM ET, Mon August 9, 2021

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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.ReplayMore Videos ...Wuhan takes drastic action to stop Delta outbreak. See what city looks like 03:25Longer 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.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."