Delta is keeping Australia on alert

This article was first published on 22nd June 2021. Up-to-date information on the current outbreak in NSW may be found here.

In recent weeks, we’ve heard of a virus able to transmit through “fleeting contact”. The newly emerged Delta strain of SARS-CoV2 seems to jump from one person to another as they share the same air for a very brief moment – for example, walking past each other, or going up and down the same escalator.

That is what authorities think has happened in the recent Victorian outbreak and the ongoing New South Wales outbreak.

This morning NSW authorities revealed 10 new locally acquired cases, all except two currently in isolation – but one of the two is a primary school student. That brings to 21 the total new cases linked to the so-called “Bondi cluster”. Among other measures, the NSW government has extended mask-wearing provisions for another seven days, through to Wednesday midnight next week.

NSW Premier Gladys Berejiklian told reporters this morning that it wasn’t a surprise to see more cases emerge, and that more are anticipated among the close contacts of existing cases.

“As [NSW Chief Health Officer] Dr [Kerry] Chant will repeat today, unfortunately, a number of people who contracted the virus have done so in a very fleeting way,” said Berejiklian. “Literally being within less than a metre within somebody but sharing the same airspace without any physical contact has still meant the virus has transferred.”

Fortunately, QR codes and CCTV footage have made contact tracing especially effective. “We are getting better at tracking contact, so we see links that would have been mystery cases previously,” says Associate Professor Hassan Vally, an epidemiologist at La Trobe University.

But the Delta variant is deemed to be up to 80% more contagious than the original strain first identified in Wuhan.

Victoria’s Deputy Chief Health Officer Allen Cheng noted that the reproduction number (R0) of the Delta variant is likely to be about 5. That means that 1 infected person would spread it to 5 others in an uncontrolled environment – with no distancing or infection control measures in place. In comparison, the R0 for the original virus was estimated to be between 2.0 and 2.5.

“We do have enough evidence to know that the Delta variant is more infectious,” Vally says. “It is not unreasonable to believe that it may take less contact between people for the virus to be transmitted.”

The Delta variant has now spread to 80 countries, and it is quickly taking over other variants. “Everywhere that it’s appeared, it outcompeted existing strains,” Vally says. “That’s classic natural selection – survival of the most infectious.”

This Delta variant has already cracked into Australia. To stop it from raging across the community, all the measures we have used so far will work, says Vally. That is high levels of testing, efficient contact tracing, isolation of positive cases and close contacts, social distancing, hand washing and mask wearing.

“It does have the potential to spread quicker, so we have to up our game,” says Vally, adding that luck also plays a huge role. In the past months, we’ve learnt that SARS-CoV-2 spreads in clusters. That means that about 80% of cases don’t pass it on to others. But a few cases are spreaders and can trigger an uncontrollable wave. “It just depends who gets infected.”

That is why rapidly achieving widespread vaccination is crucial. When the virus finds its way into the community, vaccinated people are protected from becoming severely ill. The outcome is known if we push our luck with SARS-CoV-2.

As the months go by, variants are likely to become more and more contagious. As more people gain immunity through infection or vaccination and more infection control measures are imposed, the virus is under increasing pressure to mutate to survive.

“Whilst you’ve got the virus circulating, the selective pressure will always favour a virus that becomes more infectious,” says Vally.

But the virus might also become less deadly – killing all its possible hosts will not help its survival.

“And this is how some pandemics end,” says Vally. “That’s the theory. Whether that occurs will be interesting to watch.”

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