Coronavirus: Mystery COVID-19 cluster halts hopes of early easing of Melbourne lockdown

Dangers posed by the COVID-19 outbreak that threw Victoria into lockdown have largely passed but fears of a new Delta variant are keeping restrictions in place.

A fortnight after the first cases were identified, the initial 1900 close contacts of the Whittlesea cluster were on Sunday released from quarantine – the outbreak now likely to have been contained.

But as mystery continues over how a newer West Melbourne cluster involving the more infectious Delta variant began, health authorities maintained it was unlikely Melbourne’s lockdown would be lifted before the Thursday night deadline.

Four new locally transmitted COVID-19 cases, including two confirmed at the Arcare Maidstone aged care home, have raised the state’s active community transmissions to 72.

A 79-year-old resident who lived close to two other residents previously diagnosed with Covid-19 was one of the latest cases. An agency registered nurse who last worked at the aged care centre on Saturday was the other.

Both had been vaccinated.

Victoria’s deputy chief health officer, Allen Cheng, said extensive testing and the fact three weeks had passed since the initial Whittlesea infections occurred meant concerns were easing that there may be undetected chains of transmission.

However, Professor Cheng said the “upstream” risks of a separate West Melbourne cluster revealed on Thursday to involve the Delta coronavirus variant was now the primary concern preventing an easing of restrictions.

“It is fair to say that, with the passage of time, we get more comfortable with unknown sources of cases if they have no transmission going on after one to three weeks,” Professor Cheng said.

“We always have a baseline level of concern where we don’t know where there is a case … but I think we are more worried about the origin of the Delta variant at this stage.

“For these cases that we can’t find who gave them the infection, particularly the family who returned from Jervis Bay, we are concerned about who was it that might have given them the infection and therefore could there be other infections related to that.”

Health investigators are continuing the search for answers as to how the Delta variant entered the community, trawling through genetic sequencing results from labs across the country hoping for even a partial match.

The West Melbourne outbreak grew to 10 cases infected with the Delta variant after another was confirmed overnight on Saturday. The case was a teacher at North Melbourne Primary School where 98 per cent of those tested from the tier 1 exposure site had returned negative results but would remain in quarantine. There were no new cases for the Whittlesea outbreak, which has 29 infections, while the Port Melbourne cluster rose to 30, including a person who was already isolating.

Unexpected waste water detections prompted calls for residents in Aberfeldie, Essendon, Essendon West, Flemington, Footscray, Kensington, Maribyrnong, Moonee Ponds, Parkville and Travancore to come forward for testing even if they had the mildest symptoms.