isInfectious disease experts say more focus on airborne transmission is needed to manage the spread of Covid, but they cautioned against using alarming language when describing the Delta variant.
New South Wales Premier Gladys Berijiklian described “frightening and fleeting” encounters leading to the spread of Delta in Sydney after CCTV revealed that two people crossing paths at Bondi Junction Westfield transmitted the virus.
State Health Minister Brad Hazzard described the variant as “a gold medalist when it comes to moving from person to person.”
Queensland Director of Health Dr Jeannette Young echoed the statements on Wednesday when she announced the state would close its borders to residents of Sydney hot spots.
“With the Delta variant, we are seeing a very fleeting contact leading up to the transmission,” Young said.
“At the start of this pandemic, I spoke of 15 minutes of close contact as a concern. Now it seems like five to ten seconds is a problem. The risk is so much higher now than it was just a year ago.
Not enough emphasis on airborne transmission
“Fleeting contact” is a precise descriptor that emphasizes the airborne nature of the virus, says Professor Nancy Baxter, director of the School of Population and Global Health at the University of Melbourne.
“The spread is more likely if you are close to the person [but] there is always a potential for viral particles to be in the air and breathed in by someone passing by, ”she said. This is true for both the original Covid-19 virus and the Delta variant.
After months of mounting scientific evidence, the World Health Organization officially recognized the airborne spread of Covid in April. It can occur when viral particles remain “suspended in the air or travel more than a meter”.
Laboratory studies have shown that particles of the virus can persist in the air as an aerosol for up to 16 hours.
“Because there was this resistance to recognize it, we didn’t make the recommendations that we should,” Baxter said.
Professor Raina Macintyre, head of the biosafety research program at the Kirby Institute at the University of New South Wales, said indoor airborne transmission can occur even in the absence of fleeting contact .
“Respiratory aerosols build up the same way cigarette smoke builds up,” she said.
“In an indoor space where ventilation is not adequate, an infected person could have come and gone, but the virus is still in the air. So if you walk through this area and breathe this air, you could be infected. “
Macintyre and Baxter both stress the need to focus more on airborne transmission, especially during the winter months.
“People are still kind of stuck in this hand sanitizer and hand washing mindset, when the reality is the message we need to get across is the air you breathe,” he said. Macintyre said.
“Ventilation makes the difference. If you’re hosting people, open the window. If you are driving a car with people, open the window even a little. Wear masks. It’s the shared air that matters most.
The more transmissible Delta variant is of concern, but not alarming
Hassan Vally, associate professor at La Trobe University, said that although the Delta variant (formerly known as B1.617.2) is more infectious, transmission of Covid-19 through fleeting contact was possible even with the original strain of the virus.
” Fifteen minutes [spent] less than 1.5 meters, that’s what worried us. It was just because of the odds – the more time you spend in close contact, the more likely you are to transmit this virus, ”he said.
“The general principle is this: if a virus is more infectious, then these probabilities increase. “
According to UK data, the Delta variant is 60% more transmissible among household contacts compared to the Alpha variant, which was previously the dominant strain in the UK and at least 20 other countries. The Alpha variant is estimated to be between 43% and 90% more infectious than the original Covid-19 virus.
Delta now outperforms other variants of the virus. In the UK, it accounts for around 99% of new infections. WHO Chief Scientist Soumya Swaminathan said last week: “The Delta variant is fast becoming the dominant variant in the world due to its increased transmissibility. “
Vally said: “We have to be careful with our language and continue to remember that this is essentially the same virus. “
“It’s a little more transmissible, but it behaves the same as the original virus,” he said. “All of the same behavioral interventions should work against this variant of the virus if they worked against the original ancestral strain. “
The Delta variant appears to have a similar incubation period as the Alpha variant – the average time between exposure and a household member becoming symptomatic is four days.
However, it may be a bit more resistant to vaccines than the Alpha strain and could be linked to a higher risk of hospitalization.
Dr Meru Sheel, senior researcher at Australian National University, said public health measures remain unchanged in response to the new strains.
“It doesn’t have to be a scary story,” she said.
“Of course, new variants are going to emerge, and some are going to be more contagious and others less. The public must play its part as public health measures increase and decrease according to these variations. Wash your hands, stay home if you don’t feel well, just go get tested. Wear your mask, get vaccinated if you are eligible. “
Baxter concluded: “Vaccination is a race. If there is just less Covid in circulation, there is less chance of these changes occurring that make it more effective [at spreading]. «