An alarming theory has emerged about the strain of coronavirus currently circulating in Victoria.
Health authorities identified on Monday the first cases of the latest Whittlesea outbreak in Melbourne's north tested positive for the B.1.617 strain of the coronavirus, also known as the Indian variant.
The cluster has now grown to a total of 26, with 12 new cases announced on Thursday.
One of the cases is on a ventilator in the intensive care unit while the whole state has been plunged into a seven-day lockdown.
Victoria's Acting Premier James Merlino told reporters the state was dealing with a "highly infectious" strain of the virus, with the time between catching it and passing it on "faster than ever".
"The time between catching the virus and passing it on is tighter than ever," he said.
"For some of those cases I mentioned... how long it takes between the onset of symptoms in the first and secondary case is averaging just over a day.
"Now, to put that in some perspective, the usual transmission is about five to six days. In some of these cases, within a day it’s been transmitted.
"The number of cases has doubled in 24 hours. Unless something drastic happens, this will become increasingly uncontrollable."
The variant has been leaked into Australia from returned travellers from India, with experts saying it can be anywhere from 20 per cent to 80 per cent more transmissible than other variants.
Chief Health Officer Brett Sutton said the infectious variant was one of the reasons for the increase in daily cases.
"When we see a member become infected, almost all the household is infected," he told reporters.
"It speaks to the infectiousness of this B.1.617 variant, but also the cycles it's going through.
"It really is rapid and that's led to the exponential increase."
Worrying theory about Indian variant
Imperial College London epidemiologist Professor Neil Ferguson, told a Science Media Centre briefing there were also suggestions people under 21 were more likely to be infected with the B.1.617 strain.
"There's a hint in the data that the under-21's are slightly more likely to be infected with this variant compared with other variants in recent weeks in the UK," Prof Ferguson said.
“Whether that reflects a change in the biology or reflects what’s called founder effects and the context – the people who came into the country with the virus and then seeding of infection in certain schools and colleges – that’s impossible to resolve at the moment.”
Prof Ferguson said they could not detect how severe the infection in young people was as the variant was too recent for it to be established.
Concerns 'need to be taken seriously'
University of Cambridge's Professor of Clinical Microbiology Ravindra Gupta told the briefing indications the variant posed a heightened risk to young people had to be taken seriously.
“I do think we should take these reports seriously because that’s the first sign that you have a problem," he said.
“Often if you wait too long for the right data it’s too late.
"We should be receptive to what's coming out and hopefully the countries where they're seeing this will be studying it in a rigorous way so we can get that information."
The B.1.617 variant was first reported in India in December 2020, according to Global Biosecurity research published in the Watching Brief: The evolution and impact of COVID-19 variants B.1.1.7, B.1.351, P.1 and B.1.617.
It has been found in at least 18 countries around the world.
According to the research, cases with the B.1.617 variant show unusual viral symptoms.
"Patients are presenting with abdominal pain, nausea, vomiting, diarrhoea and hearing impairments," it said.
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