Fears of a new Delta variant of COVID-19 are keeping restrictions in place in Melbourne, despite the fact that the outbreak of the Whittlesea cluster which was first identified a fortnight ago seems to have been contained.

Victoria recorded nine new locally acquired cases of COVID-19 on Monday, which – in addition to the two cases reported in an aged care home in Maidstone on Sunday – take the official tally to 11.

There are now 94 active cases across the state.

Victoria’s Deputy Chief Health Officer Allen Cheng said extensive testing and the passing of three weeks show that initial concerns for the Whittlesea cluster had now eased.

“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.”

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Mystery surrounds a newer West Melbourne cluster which is where the more infectious Delta variant of COVID-19 began. As a result, it is unlikely that Melbourne’s lockdown would be lifted before the Thursday night deadline as had been previously hoped.

There were four locally transmitted cases of COVID-19 of which two were confirmed at Arcare Maidstone aged care home yesterday. The latest cases at Arcare concern a 79-year-old who lived close to the two other residents, aged 89 and 99, which had tested positive for COVID-19. A nurse, whose last shift had been on Saturday, also produced a positive test.

The resident and the staff member – both asymptomatic – had been vaccinated. Arcare Chief Colin Singh said that the nurse had received the first dose of the vaccine and teh resident had received both doses of the Pfizer vaccination. He said the resident would be transferred to hospital despite showing no symptoms.

Long queues for the vaccine have formed as Victorians have rushed to be vaccinated.

Acting Premier James Merlino on Sunday had said the rollout was crucial to avoiding future lockdowns.

“This is a race and we need to get as many people vaccinated as quickly as possible,’’ he said.

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Despite Mr Merlino’s statements, Victoria’s chief health officer has warned there is no ‘magic number’ of people getting vaccinated before future lockdowns are ruled out.

“There isn’t one single magic number,” Professor Cheng said.

“Once you get up to much higher coverage rates, then it makes a whole lot of things easier.

“We may not need the intensity of restrictions. We may be able to only do contact tracing without having to do other things quite to the same level, and that is the benefit of vaccination.”