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.