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South Australian premier Steven Marshall has said part of the reason for the state’s sudden and strict six-day lockdown is that the state is facing “particularly sneaky strain” of Covid-19 [SARS-CoV-2].
“[It’s a] highly contagious strain … and if we don’t get on top of that very, very quickly it will get away from us and that will be disastrous for us in South Australia,” he said on Thursday.
“We have a particularly difficult strain of the disease, which is showing no symptoms for people who become infected. The other thing that we know is that the incubation period for this particular strain is very short, and it can be down to 24 hours.”
A more infectious strain of the disease would be concerning, due to the potential for more rapid spread and implications for the efficacy of vaccines. Marshall told ABC radio: “The elements of this are quite frightening … It’s quite different than anything we’ve seen before.”
What evidence is there that this strain is more infectious?
Dr Adam Taylor, an emerging viruses researcher with the Menzies Health Institute Queensland, said without sequencing the genetic material of the virus circulating in the South Australian outbreak, not much could be said about whether this was actually a unique, infectious strain.
The evidence – that it has a very short incubation period, is sometimes transmitted from surfaces, and displays no symptoms for some people who become infected – are all characteristics of the major virus strain circulating globally, he said.
“To have a completely new strain requires mutations in the virus genome to cause changes in the way the virus interacts with its hosts and the environment,” Taylor said.
“Only through sequencing the virus responsible for this outbreak and subsequently studying its behaviour in the lab will we begin to understand the virus at the centre of the South Australian outbreak.”
Taylor said this did not mean that authorities were wrong about the outbreak being serious and concerning.
“But the characteristics they describe, such as ‘highly contagious’, may be a result of how the virus is interacting with humans, rather than a change in the virus,” he said.
“For example, the rapid spread of the virus in this outbreak may be due to a super-spreader event, possibly centred on the pizza parlour. This is a more likely scenario than the rise of a new virus strain. Until we see the genome sequence of the virus and confirm its behaviour experimentally, we cannot be sure we’re dealing with a new strain.”
Guardian Australia asked the South Australian health department for clarification of Marshall’s comments and the evidence it is based on, but is yet to receive a response.
But a professor of infectious diseases and immunology at Griffith University, Nigel McMillan, said: “There is no genomic data for the scientific community to verify such a claim, where a new strain has a specific definition.”
So why is Marshall saying it is a more infectious strain?
“What’s happening I think is similar to what happened with the Crossroads Hotel outbreak in New South Wales,” says infectious diseases physician and professor with the Kirby Institute Gregory Dore.
In July the NSW chief health officer, Dr Kerry Chant, said of the Crossroads Hotel outbreak: “What’s been interesting is we’ve seen some acquisition which has been very short. So people have developed the symptoms more towards the one-day period than the 14.”
The comments were similar to those made by Marshall on Thursday.
But Dore said if health authorities identified a cluster and as a result rapidly began to test and contact trace a significant number of people, they would also pick up asymptomatic cases and people who were only recently infected. This skews the data to make it seem like people are becoming infected more quickly.
“The strategy in South Australia is right. I’m really supportive of that great contact tracing and isolating contacts and doing widespread testing and asymptomatic testing,” Dore said.
“But the results are not that reflective of some sneaky strain suddenly launching itself upon South Australians. Now it will be a slightly different strain most likely to the one in Victoria as viruses do change and it has probably come from a different country.
“But globally there haven’t been huge shifts between strains to the extent that makes some more virulent or pathogenic. In fact this virus actually seems to change more slowly than the flu. That’s good news for a vaccine for Covid-19.”
What do we know about Covid strains circulating across the world?
“For now, SARS-CoV-2 and its variants can still be considered as a single ‘virus’,” a virologist at the UQ child health research centre at the University of Queensland, Associate Prof Ian Mackay, said.
“It’s like all of the world’s human genetic diversity still sitting under the umbrella of one species.
“Most of what we read about in terms of ‘new strains’ is mostly about small genetic and sometimes amino acid [affecting the protein] changes, the impact of which is either unknown or not obvious.”
But he said as the virus spread in different areas it continued to evolve and so vigilance was essential.
Source: The Guardian
Keyword: SA Covid lockdown: experts doubt state suffering ‘particularly sneaky strain’ | Australia news