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“Everybody has body heat, and that updraft of hot air keeps whatever’s coming out of our mouth elevated for a period of time.
“If we’re busy rushing past people, that also causes a lot of air turbulence and you can have the virus suspended.
“We’re very lucky with our geographical distribution, and we don’t really have the huge ultra-megacities like some other countries.”
Flinders University epidemiologist Emma Miller said the couple had visited venues with sustained close contact with other people, like at the movie theatre.
But she said a bullet was dodged because of three important factors that must not have all been in play.
“One, the level of viral shedding that’s going on in an infected person. Two, the circulation of air. Three, the proximity and susceptibility of the people in the area,” she said.
“All those factors have to come into play, and they explain why sometimes we see really easy transmission with very little contact, and yet sometimes really low transmission when there were opportunities for there to be.
“How close were they to people? How good was the ventilation in the area? Were people around them staying at a good distance, were they wearing masks? That may explain what happened.
“We’re starting to get used to this tale with this new variant that fleeting contact can cause a case — and that is absolutely true, but there are factors that are involved in a transmission.”
A Covid-19 testing clinic staff member swabs a client in Brisbane. Picture: NCA NewsWire / Dan PeledSource:News Corp Australia
She agreed it seemed the couple had low levels of viral shedding on the trip despite being in an infectious period while in NSW.
She noted testing was still being done in Queensland and the state was on “tenterhooks” as results continued to come back, but that NSW appeared to have escaped unscathed.
“They were not superspreaders and it sounds like they weren’t that ill even if they were symptomatic, because they were participating in all those activities,” she said.
Monash University Epidemiological Modelling Unit head James Trauer said that a small number of Covid patients were responsible for a lot of further infections.
At the same time, many infected people caused zero further transmission.
NSW and Queensland got lucky in that the Melbourne couple do not appear to be superspreaders.
“Part of that is just the nature of the virus,” he said.
“You get a handful of people who tend to be extremely infectious and then you get a large proportion of people who are not infectious at all.
“The way that plays out is that you can have a positive case that can very easily die out, but if it does take off you can have rapid explosive outbreaks.”
He also said that the way states reacted to events like the Melbourne couple was likely to change as more Australians became vaccinated.
Once over 60 per cent of the population received the jab, two cases should not be a cause for widespread alarm, Associate Professor Trauer said.
Queenslanders are urged to get tested if they have any Covid-19 symptoms as the search for any follow-on cases from an infected Melbourne couple that entered the state continues. Picture: NCA NewsWire / Dan PeledSource:News Corp Australia
It was only because states like Queensland had achieved zero cases that life was able to return almost to normal, which is why there was so much focus on keeping cases at zero.
“The real concern is that we’re still essentially going for an elimination strategy, even though we seem in Australia to have this aversion to ever calling it that,” he said.
“I feel like we’re not doing enough to communicate to the public that the reason we’re doing this is because when we get totally to zero you can go so much back to normal.
That is working at the moment, and should work up until we get vaccinated — and then we change the approach.
“Then we should accept some transmission in the community and we should really be looking to move away from lockdowns.”
The first to test positive in the Melbourne couple who travelled to Queensland returned a positive result on June 8 after being tested because it was required for the husband’s new job.
The woman had been experiencing symptoms since June 3.
The pair relocated while Melbourne was in lockdown and the whole state was considered a hotspot by Queensland, meaning any Victorians who crossed the border were supposed to enter hotel quarantine for 14 days.
Victoria’s Covid-19 Commander Jeroen Weimer on Saturday said “lengthy” interviews had been conducted with the couple and their exposure sites in Victoria had been traced back to May 18.
Their destination in Queensland was Caloundra on the Sunshine Coast where they stayed with family.