A nurse who has tested positive while working in a Covid-19 ward also worked shifts at a second Melbourne hospital, it has been revealed.
Victoria's testing commander Jeroen Weimar said he was "exceptionally concerned" about the lapse.
He confirmed the nurse was looking after three Covid patients at Epping Private Hospital.
It has emerged she also worked two shifts at Northern Hospital on June 11 to 12.
There are now 22 Northern Hospital staff who are isolating for 14 days, as well as nine primary close contacts of the nurse at Epping Private.
Nurse should have only been working on Covid ward
Mr Weimar said he had meetings on Wednesday night with the chief executives from Epping Private and Northern Hospital.
"I'm exceptionally concerned — we have very clear expectations and strong requirements of the designated COVID wards," he said.
"One of those expectations is that staff are dedicated to that particular ward.
"That should not have been allowed to happen.
"This appears to be an operational error being made at Epping Private ... it is disappointing, I'm very unhappy about that situation."
Melbourne health staff isolated
He added another 25 staff had isolated after the nurse's positive test and 22 of those had returned negative tests.
The nurse also visited the northern vaccination centre on June 14 for her final dose and 30 people there - five staff and 25 patients - are isolating for 14 days.
Tests are underway to determine how the nurse caught the virus, with Mr Weimar noting she had looked after three Covid-19 patients from the Arcare Maidstone aged care facility at Epping Private.
She was among three new cases announced on Wednesday.
Victoria recorded no new locally acquired coronavirus cases on Thursday, ahead of a further easing of restrictions across Melbourne and the regions on Friday.
The Health Department on Thursday confirmed just one new Covid-19 case involving a returned traveller in hotel quarantine.
The total number of active cases in the state is now 54.
Easing of restrictions for Melbourne
Some 25,635 Victorians were tested in the 24 hours to midnight on Wednesday while 15,610 received a COVID-19 vaccine dose at state-run hubs.
It comes ahead of an easing of restrictions in Melbourne and regional Victoria from Friday.
Under the latest changes, Melbourne residents will be able to travel to regional Victoria with the removal of the 25km journey bubble, host two adult visitors plus their dependents per day and gather outdoors in groups of 20.
Masks will remain mandatory indoors but will only be required outdoors when social distancing isn't possible.
Businesses such as gyms and indoor entertainment venues will be able to reopen, while density limits at offices, cafes, restaurants and pubs will increase.
In regional Victoria, the home visit cap will increase to five adults plus their dependants per day, while up to 50 people can gather outdoors.
Acting Premier James Merlino says restrictions could ease further in a week's time if Covid-19 cases remain low.
Chief Health Officer Brett Sutton said there still may be undetected cases in the community and urged people not to slacken off on following rules.
"It's really tough. This is 16 months into a pandemic. There is no question that people are over this," he said.
Meanwhile, the state government has ramped up the range of experts who will be on hand to give advice about its planned mRNA vaccine manufacturing facility.
US immunologist and virologist Barney Graham, whose ground-breaking research on mRNA helped lead to the development of the Moderna vaccine, will join the nine-person advisory group.
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