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Medical experts have urged caution regarding claims the Covid-19 variant in Victoria is spreading significantly more quickly, after the acting premier, James Merlino, stated the virus was “running faster than we have ever recorded”.
“The usual transmission is about five to six days [but] in some of these cases, within a day it’s being transmitted,” Merlino said on Thursday as he announced the state’s lockdown would begin on Friday. “The number of cases has doubled in 24 hours. Unless something drastic happens, this will become increasingly uncontrollable.”
The specific variant involved in the outbreak is the B1617.1 variant, first identified in India. It is not the most infectious variant in India, which is B1617.2. The chief health officer, Prof Brett Sutton, said it is, however, “at least” as infectious as the B117 variant prevalent in Britain.
But despite Merlino’s concern about as little as one day between infection and transmission, the Kirby Institute’s Prof Greg Dore said there was no clear evidence variants of concern, including the one involved in Victoria’s latest outbreak, shorten incubation period or the serial interval.
In epidemiology, the serial interval is the time from illness onset in the primary case to illness onset in the people they have infected, while incubation period is the time from an individual being infected to the onset of symptoms.
Dore said some variants of concern with higher viral levels could influence the serial interval, but would not change the average from five days to as little as one day.
“More data could show a slightly shortened serial interval,” Dore said. “But it is more likely increased infectiousness of some variants of concern is related to higher viral level,” he said.
The higher the viral level, the more infectious someone is, increasing the chance of spread.
“[Among] other factors that ‘shorten’ the serial interval artificially is rapid contact tracing, which leads to close contacts being swabbed before symptoms even develop, which we see when there is high-level testing of contacts,” Dore said. “And, cases with shorter intervals are detected earlier in an outbreak.”
Similar concerns had been expressed by other premiers about a shortened incubation period during outbreaks in their states involving other variants, including in the early stages of the NSW Crossroads hotel outbreak and in South Australia, where cases were linked to a pizza bar.
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.”
In November, the South Australian premier, Steven Marshall, said part of the reason for the state’s sudden and strict six-day lockdown was because of “… 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 professor of infectious disease with the Australian National University, Peter Collignon, said it turned out “that wasn’t true”.
“We do need to be careful about the way we describe spread,” Collignon said. “It’s fair to say there are variants behaving differently but not to be dogmatic. There’s enough fear and catastrophising as it is.”
What had not changed, Collignon said, was that the virus and all of the variants spread the same way. “And that means the public health basics still hold, including hygiene and social distancing,” he said. “Plus, the importance of getting vaccinated.”
He agreed with Dore that the virus appeared to be spreading faster as the contact tracers were working fast, finding people, testing them and putting them into quarantine, sometimes even before they developed obvious symptoms.
“If you look at India and even England, where this variant is now also spreading, I am not aware that the incubation period of five days has changed that much, though there are always outliers and super-spreaders,” he said.
“With the UK variant, the median incubation period was the same though people were infectious slightly longer, for five days on average rather than four. Will this be similar in the case of the variant in Victoria? Well, there is simply not enough data yet to say.”
Associate professor of microbiology at RMIT University Taghrid Istivan said nonetheless the B1617.1 variant is more infectious than others and the lockdown was essential to control it.
“It is clear now that we are dealing with a highly contagious variant of the virus, which must be dealt with before it is too late,” he said.
“I feel that more measures should have been put in place earlier in May, since the first case from the Wollert man who got infected in the quarantine hotel in South Australia was detected.
“Given that we are heading into winter, in addition to the hesitancy in getting the AstraZeneca vaccine by older eligible recipients, and that many aged care residents haven’t yet got their first Covid-19 shot yet, and with the fast-growing number of positive cases detected in the past two days, I hope it is not too late.”
Source: The Guardian
Keyword: Victoria’s Covid outbreak: is the variant in Melbourne spreading more quickly? | Melbourne