A family infected with Covid who travelled to NSW's south coast have been confirmed to have a different virus variant than that causing Melbourne's outbreak, health officials said.
Victoria's Chief Health Officer Brett Sutton told reporters on Friday authorities had detected the Delta variant of the coronavirus, which had become the predominant one in India.
"It is a variant of significant concern," he said.
"It has obviously had very high transmission potential, because it spread extremely rapidly across India to become the predominant variant, almost the exclusive variant there.
"And surroundings countries – Nepal, Bangladesh, Sri Lanka – are also affected by a significant uptick in cases related to the variant.
"It does appear to be the most significant in terms of transmissibility."
Professor Sutton said there were suggestions the variant caused greater illness among children and there were concerns for that reason.
It is believed to be the first time it has been detected in Australia.
Professor Sutton added the new variant detected in two cases was unrelated to all other cases in the Melbourne cluster so far.
"It is a concern that it is not linked to other cases, but we are chasing down all those primary case contacts for that family and looking into where it might have been acquired," Professor Sutton said.
"It has not been linked to any sequence cases across Australia from hotel quarantine or anywhere else that it is not linked in Victoria or any other jurisdiction"
The other new case is a primary close contact of another confirmed case.
The four new cases take Victoria's current outbreak to more than 60.
Two false positives detected
It comes after Thursday's confirmation that two earlier cases in the outbreak had been ruled false positives.
The two suspected "fleeting" transmission cases of coronavirus that are now false positives had been part of the justification for Melbourne's lockdown extension.
Victorian Acting Premier James Merlino said despite the two false positives, there were no immediate plans to shorten Melbourne's lockdown.
"Our answer on that hasn't changed and nor should it," Mr Merlino said.
"The advice from public health remains the same.
"It (false positives or false negatives) has been a rare occurrence, but it has been a feature, when you do 100s of thousands of tests."
Health authorities initially thought a woman caught COVID-19 at a Metricon display home at Mickleham, and believed a man similarly picked up the virus at Brighton Beach Hotel.
An expert medical panel found that was not the case.
The COVID-free pair and their primary close contacts will be released from isolation and exposure sites reclassified, including all in Anglesea along the Great Ocean Road.
The Metricon display home and Brighton Beach Hotel remain linked to other confirmed cases and will remain listed as exposure sites.
There are now 358 sites where exposure to the virus may have occurred.
On Friday morning the Health Department issued a statement, saying there are still eight cases of transmission through passing contact.
It added there are still five exposure sites where the virus has spread through people who do not know each other.
Do you have a story tip? Email: firstname.lastname@example.org.