Sydney remains on a knife edge. NSW Premier Gladys Berejiklian has for days kept her nerve and resisted a shutdown of Australia’s global city, the default reaction of other premiers faced with even a handful of cases.

Instead Ms Berejiklian is trusting in “the best contact tracers on the planet”, as she calls them, to keep pace with COVID-19’s delta variant, a nasty adversary which hangs in the air and apparently can spread 50 per cent faster than its predecessors through the unvaccinated, the unmasked, and anyone passing too close to an infected person.