“Most recently, the data just coming out of the UK now as they look at their own outbreaks, they’re seeing higher hospitalisation rates.
“You’re more than twice as likely to be hospitalised if you have that variant and 1.6 times as likely to be in an emergency department within two weeks.
“The vaccine still works against the delta strain, but the battle is against that level of transmissibility and the concern that there is also potentially greater severity.”
Melbourne University professor Tony Blakely said the emergence of the delta variant was a real setback.
“This is currently, as best we know, the most infectious virion around the world and it’s taking over places like the UK.
“It is roughly twice as infectious as last year’s variant.
“We’ve got two clusters happening now. And I really want to know where these people with the delta variant got it from. So basically it is an action replay of what we’ve been doing the last 10 days but with a new cluster.”
Three hundred primary contacts have been identified with the two families, with 70 per cent testing negative so far. An estimated 130 contacts have also been identified by NSW, ACT and Commonwealth officials after the family camped in the section of Jervis Bay which is a Commonwealth territory.
The father of the family who camped at Jervis Bay tested positive on Tuesday week and his new sequencing results came through Thursday evening.
Seven cases across the two families have now been revealed to have the delta variant. The suspected transmission between two Year-5 children of the two families at a North Melbourne school sparked concern about child and school safety.
“There are some anecdotal reports of greater severity of illness in children, as well as potential increased transmissibility in children, so we’ve got concerns for that reason,” Victorian chief health officer Brett Sutton said.
Despite this anecdotal evidence, Professor Sutton said the evidence was children usually only had mild symptoms.
“Kids don’t need to be afraid here. We need to just do everything to make sure no further transmission occurs.”
Earlier UK research found the delta variant to be about 50 per cent more transmissible than the UK variant. Because of this higher transmissibility, the World Health Organisation has declared the delta a “variant of concern”.
Professor Ben Howden, director of microbiological diagnostics at the Doherty Institute, said the World Health Organisation classified delta and kappa as variants of concern in May.
“But as of last week kappa was downgraded and is now a variant of interest. Australia considers both as variants of concern currently – this is under active monitoring and will be re-assessed on Monday,” Professor Howden said.
Professor Sutton admitted yesterday the discovery of the delta variant in a new chain of transmission without a known source will influence lockdown decisions.
“It has obviously had very high transmission potential, because it spread extremely rapidly across India to become the predominant variant.
“The fact that it is a variant different to other cases means it is not related, in terms of transmission, with these cases.
“We certainly have to identify what the origin is. It will make a huge difference if there are unknown chains of transmission that reveal themselves in Melbourne or in another jurisdiction.
“That will make a difference.”
Authorities said they are re-examining records of positive cases, any diplomatic travellers and ships.
“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,” Professor Sutton said.
However, Professor Bennett said the “positive in this is that we’ve had it appear overlaid against a full outbreak investigation where we’ve had extraordinary testing in Melbourne, so it’s unlikely that there are a lot of cases out there that we don’t know about.”
“It suggests that if we’ve got a very local cluster, that it’s a recent introduction, but where it came from, no one knows,” Professor Bennett said.