Health authorities reveal four theories on how Delta variant spread in Melbourne

Victorian authorities have revealed four theories for how the contagious Indian Delta variant seeped into the Melbourne community.

Health officials are investigating “four main theories” on how the highly contagious Covid-19 Delta variant – infamous for its rapid spread across India – seeped into the Melbourne community.

It comes after Victorian contact tracers found a genomic link overnight between a returned traveller who entered the state’s hotel quarantine system on May 8 and the West Melbourne Delta cluster.

The traveller arrived from Sri Lanka on May 8 and tested positive that same day before being transferred from the Novotel Ibis quarantine hotel to the Holiday Inn health hotel May 14.

He completed his quarantine and was released on May 23.

Victoria deputy chief health officer Professor Allen Cheng says there are four main theories on how the Covid-19 Delta variant seeped into the Melbourne community. Picture: NCA NewsWire / Paul Jeffers

Victorian deputy chief health officer Allen Cheng said authorities were now investigating how the Delta variant spread from hotel quarantine to the wider community in Melbourne.

He said the first possibility was the case was infected by another passenger on the flight to Australia, and that other infected person has then transmitted the virus to someone in the community.

A second working theory was the case transmitted the virus after he left hotel quarantine.

Professor Cheng said a third possibility was the case transmitted to a staff member “somewhere along their journey from the airport to the first hotel”, and that staff member then spread the variant on.

The fourth possibility was the case transmitted to a hotel resident who has then transmitted to the community after their quarantine stay.

“We have addressed all of these and some of these are still ongoing investigations,” Professor Cheng said.

“In terms of the first possibility … we have reviewed the details of the 24 people who arrived on the same plane.

“They were all designated close contacts because this gentleman tested positive soon after arrival and we have confirmed that they all tested negative before leaving quarantine.

“To address the second possibility about the case transmitting after his time in hotel quarantine, we have reviewed the swab and serology details of the case and we have determined that he was correctly cleared.

“So he was not felt to be infectious when he left isolation at the health hotel.

“However, we are still following up the contacts of this gentleman after his discharge to make sure that there was no transmission after that.”

Melbourne’s lockdown is scheduled to end on Thursday. Picture: NCA NewsWire / Paul Jeffers

Professor Cheng said the revelation was “significant” as it now meant the Delta variant did not exist in Melbourne before May 8.

“It means there is unlikely to be very widespread transmission for a long period of time before this outbreak was detected in North Melbourne,” he said.

“This does change our understanding of the sequence of events.

“We had been working on the likely scenario that the family that had been in Jervis Bay (NSW) had been the first familiar case in this outbreak.

“This does suggest it could be the other way round. We are investigating the possibility that the second family was the first to get infected and then have transmitted it to the other family.”

Victoria recorded two new local cases on Tuesday – there are 92 active cases across the state.