Highly infectious Delta variant spreads in Australia's Victoria

Australia's second-most populous state Victoria has reported an increase in locally acquired Covid-19 cases as authorities hunted for the source of a highly infectious variant that has been detected in a new cluster.

Five new local cases were reported, taking Victoria's total to 70 in the latest outbreak, including one recovered case, as the state capital Melbourne entered its second weekend of a hard lockdown, due to end on June 10.

Curbs were eased for the rest of the state on Friday.

Saturday's count was up from four new locally acquired cases on Friday.

Authorities on Friday were alarmed after detecting the highly infectious Delta Covid-19 virus variant for the first time in Australia, sparking concerns cases could spike.

The new Delta variant cluster has grown to nine active cases, up by two from Friday including a case transmitted at a workplace.

"The next few days will be critical, because we'll see where this one goes," state testing commander Jeroen Weimar told reporters.

READ MORE: 'Problem for whole world': WHO scientist says India variant more contagious

Fast- spreading virus strain 

The Delta variant, which has been classified by the World Health Organisation (WHO) as among the four Covid-19 variants of concern due to evidence that it spreads more easily, is one of the virus variants first detected in India.

Victoria's chief health officer, Brett Sutton, said the Melbourne lockdown could be lifted later next week as long as all cases have been tracked down, even if the source of the Delta variant had still not been found.

"It is a challenge -- the transmissibility, the secondary attack rate being 50% greater than the Alpha variant does mean you can get a large number of people within a home testing positive and you can get those transmissions in other settings more readily. But we can still manage all of that," he said.

Infectious diseases expert Sharon Lewin, director of the Doherty Institute which is handling genomic testing of the virus, said her strong hypothesis was that the Delta variant had come into the community through hotel quarantine, but no match had been found yet.

Snap lockdowns, regional border restrictions and strict social distancing rules have helped Australia rein in prior outbreaks and keep its Covid-19 numbers relatively low at just 30,150 cases and 910 deaths.

Victoria's outbreak, which began on May 24, has spurred people to join long queues for vaccinations following a slow rollout since February. So far, 20% of the adult population has had a first dose of a Covid-19 vaccine.

READ MORE: Here is what you need to know about India's Covid-19 B.1.617 variant