July 21, 2021 People walk in front of the Sydney Harbour Bridge as the state of New South Wales continues to report low numbers for new daily cases of the coronavirus disease (Covid-19) in Sydney, Australia, on Aug 19, 2020. Reuters Each time Covid-19 has flared up, Australia ’s major cities have used strict lockdowns to battle cases back down to zero. As the pandemic wreaked havoc elsewhere, the country’s “zero Covid” approach prevented deaths and major disruption to everyday life for much of the past 18 months. The Delta variant is now challenging the effectiveness of that approach like never before, as outbreaks linked to the mutant strain in three state capitals have some experts deliberating whether elimination is no longer possible – even as more than half of the country’s 25 million people were under lockdown on Tuesday in a bid to curb its spread.