CBD SITE SHUT DOWN: Outbreak grows, fears of hyper-infectious strain
More than a hundred people will spend the next 14 days in quarantine after a single covid case – from a mutant strain – triggered a massive public health response.
Two of today’s five new cases were from the Delta strain – a highly infectious variant that spreads twice as fast as other strains.
One of the positive cases is employed by Probuild, a large construction company that runs building sites in the CBD.
The site the employee had worked on was locked down last night, with 170 people ordered into isolation.
Health authorities have confirmed the Delta strain has been found in nine people in Melbourne — including four children.
Victoria recorded five new locally acquired cases of coronavirus today, with 70 cases now linked to the state’s outbreak, including one recovered case.
Victorian Health Minister Martin Foley said two of today’s cases, both from the same household, were currently unlinked.
The three remaining cases are linked to known outbreaks.
Mr Foley said continuing uptake of vaccines across the state was the “off-ramp” for Victoria’s lockdown.
Victoria’s chief health officer Professor Brett Sutton said it was “gratifying” that three of today’s five cases had already been in isolation while testing positive.
The remaining two cases had not been linked yet but they had spent time around the shopping centres in Craigieburn and Epping, two known coronavirus hotspots.
Prof Sutton also addressed the upcoming antivax protests, expected to hit Melbourne today.
“It’s hugely unfortunate that there’s that sentiment in anyone … as an individual you’re free not to get it, which I still find some discomfort in, but it is your choice,” he said.
“But do not get in the way of those Victorians trying to get vaccinated.”
Testing Commander Jeroen Weimar said the state was “most concerned” about a new cluster of nine cases – which are all from the Delta strain.
The two new cases today are both Delta cases but Mr Weimar said authorities were “establishing” a ring around the boutbreak.
Prof Sutton said, despite contact tracers still not knowing where the Delta outbreak came from, authorities could still have confidence to ease restrictions next week.
“If we only have those downstream cases and nothing else emerges, I am confident that those pillars of public health response, the contact tracing and the rings of control that we put in place, we will manage this,” he said.
“It is a challenge, the transmissibility, the secondary attack rate being 50 per cent greater than the Alpha variant, does mean that you can get a large number of people testing positive, you can get transmissions in other settings more readily. But we can still manage all of that.”
Worrying coronavirus strain around 50 per cent more infectious
“The Delta variant, this new cluster that was reported yesterday, is the dominant in the UK, and they’ve had a little bit of Kappa virus infection,” Professor Lewin began.
“From that country, the data is really good and the genomic sequencing is frequent. We do know that both of those variants are more infectious than the UK variant, which is now called the Alpha variant,” she explained.
“The estimates are that they’re probably about double as infectious. So, for every person that one person would have infected – two people, previously – they’d perhaps infect double that now.”
She added that the severity of illness was “a lot less clear” at present, and currently based on anecdotal reports.
“You really need some very systematic data collection to prove disease severity, and I’m not sure we’ve seen that yet.”
“But the same measures still will work, meaning – test, trace, isolate, masks – all the usual things that we use to stop transmission will still work here,” Professor Lewin said.
What is the Delta variant?
The Delta variant spread extremely rapidly across India to become the predominant variant in that country.
“Indeed almost the exclusive variant there and in surrounding countries — Nepal, Bangladesh (and) Sri Lanka,” Professor Sutton said.
“All are also affected by a significant uptick in cases related to that variant.
Very high transmissibility potential is the main concern.
There are some anecdotal reports of greater severity of illness in children, as well as the potential increase in transmissibility among children.
“We’ve got concerns for that reason,” Professor Sutton said.
Stuart Turville, from the immunovirology and pathogenesis program at UNSW Sydney’s Kirby Institute, said the number of Delta cases was increasing globally.
“Like what we have seen with Alpha in early 2021, it just means we will see more Delta cases in quarantine and that if there is a breach, it will be highly probable to be that variant,” he said.
What is the key difference between the Delta and Kappa strains?
Authorities say the Delta strain appears to move more quickly at “casual contact” sites.
“I’m not saying it has magical qualities, but we have noticed five exposure sites where transmission has occurred to seven individuals, I believe, who have had less than that usual prolonged indoor home, work, face-to-face settings, or indeed restaurant settings,” Professor Sutton said.
Dr Turville described the Delta strain as the genetic “cousin” to Kappa.
“The key difference is that it has a fitness gain that enables the virus to bind cells better,” he said.
“In the lab under controlled conditions, we do see Delta to be approximately 1.4 times fitter than Kappa.
“While this is a laboratory observation, the displacement of Kappa by Delta in India does support it to be a fitter variant in populations where vaccine immunity is low.”
How do the viruses get their names?
The World Health Organisation recently decided to simplify the virus names with Greek numerals, Alpha, Beta, Gamma, Delta, to avoid stigma.
Australia’s chief medical officer Paul Kelly said this was the third attempt.
“One was where they were first being found, the second was a long series of numbers and letters, which was becoming difficult to remember — even for epidemiologists,” he said.
How the variants respond to vaccines?
When asked about the efficacy of Pfizer and AstraZeneca vaccines currently being rolled out in Australia against Delta and Kappa, Professor Lewin said data from the UK suggested there was high protection against both.
“We measure effectiveness against the vaccines in two ways. You can use laboratory tests, or see how the vaccine works in practice,” she explained.
“We know a lot about the Delta strain with the vaccine in practice, again from the UK where, after the second dose of the Pfizer vaccine, 80 per cent protection against symptomatic Covid and, after the AstraZeneca vaccine, 60 per cent protection against symptomatic Covid.
“They haven’t reported the protection against severe disease but, based on other studies, we expect that the protection would be very high against severe disease, which is what we really worry about.”
She added that data surrounding the Kappa variant was not as robust.