Virus experts have rubbished claims a super-strain of COVID-19 is behind South Australia's new coronavirus outbreak.
State authorities claimed on Wednesday the new outbreak – which has infected 23 people and forced the state into a harsh six-day lockdown – was a "frightening" new strain of the virus that was more contagious and likely to spread silently without causing symptoms.
An electron microscope image shows the SARS-CoV-2 coronavirus (yellow) emerging from the surface of cells (pink) cultured in a US National Institutes of Health lab.Credit:AP
Genetic data from SA's cases, which could reveal a new mutation, has not yet been released.
In the absence of that data, experts said claims of super strains stretched scientific credibility given they had not been detected anywhere else in the world.
"Rubbish," wrote Professor Greg Dore, an infectious diseases physician and epidemiologist at the Kirby Institute, on Twitter.
He told The Age and The Sydney Morning Herald it was more likely South Australia was simply misinterpreting its own test results.
"The virus has not changed at all. It's just the detecting strategy," he said.
SA Chief Public Health Officer Nicola Spurrier told media on Tuesday the virus circulating in South Australia had a "very, very short incubation period".
"That means when someone gets exposed, it's taking 24 hours or even less for that person to become infectious to others," she said.
SA Chief Health Officer Nicola Spurrier hopes the state’s “double ring fence” approach will ensure the lockdown ends as scheduled.Credit:Getty
"The other characteristic of the cases we've seen so far is they have had minimal symptoms and sometimes no symptoms but have been able to pass it on to other people."
SA recorded no new cases of coronavirus on Thursday, as the state woke to its first day of a harsh six-day lockdown, which has closed schools and businesses, and prohibits all outdoor exercise.
South Australian Premier Steven Marshall said people had "woken up to a very different SA today", but the alternative could see the virus spread further and an extended lockdown later on.
Mr Marshall initially described the virus as a "particularly sneaky … highly contagious strain". On Thursday, he went further: "The elements of this are quite frightening. It's quite different than anything we've seen before."
He also claimed the particular strain of the virus was more likely to be transmitted on surfaces. That appears to contradict recent findings that airborne spread is more likely than surface contamination.
But multiple experts said a new, more dangerous strain emerging in South Australia was extremely unlikely.
South Australian Premier Steven MarshallCredit:Kelly Barnes/Getty Images
Compared to some other viruses, SARS-CoV-2 – the virus that causes COVID-19 – mutates very slowly. It has not yet changed enough to have multiple strains, said Associate Professor Ian Mackay, a virologist based at the University of Queensland. "This virus is really one strain – SARS-CoV-2."
A form of the virus with a small mutation that is moderately more infectious in laboratory tests has been the most prevalent version of the virus in Australia since at least August.
And many scientists are skeptical that surface spread is playing a major role in the transmission of COVID-19.
"I was expecting surfaces and hands to be a bigger factor than I think the data suggests," said Professor Peter Collignon, a leading microbiologist at the Australian National University.
He said there was "no evidence" dramatically different strains existed.
"This idea of a one-day incubation period and all the characteristics being put to it are very unlikely to represent a new strain."
It typically takes between two and 14 days for a person infected with COVID-19 to show symptoms. There is then typically a gap of about three days between them showing symptoms and when the person they infected falls sick – known as the serial interval.
It would be unusual if either of those gaps had narrowed to just 24 hours, scientists said.
However, the state has been aggressively testing contacts of infected people even if they are not displaying symptoms.
This means testers are more likely to pick up new infections earlier. That would give health authorities the impression the virus was moving more quickly, when it had not actually changed its behaviour at all.
Most testing strategies around the world focus only on people with symptoms. Because SA is testing people without symptoms, they are more likely to pick up both asymptomatic cases and ill people before they develop symptoms.
"It artificially elevates the asymptomatic proportion of cases, and it shortens artificially the incubation period," said Professor Dore.
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