Covid: How Delta exposed Australia's pandemic weaknesses

For the past year, Australia has been coasting along almost blissfully detached from the global pandemic. It had achieved a "Covid normal" where people could visit restaurants and nightclubs and join crowds at festivals and theatres.

The country's strong Covid defences - border closures and mandatory quarantine - worked 99.99% of the time.

When cases did leak, officials acted quickly, locking down cities and chasing every infected contact.

Sydney - Australia's biggest and richest city - managed to avoid regular snap lockdowns helped by a "gold standard" contact-tracing system.

But in the past fortnight, the Delta variant has managed to breach the city's defences. In one week, positive cases have ballooned to more than 100.

By Friday 25 June, officials conceded the need to put Sydney into lockdown. By the following Monday, the crisis had became a national one - with outbreaks in four states and territories.