Super spreaders stand in way of virus elimination Luck and lockdown
ELIMINATING COVID-19 in Australia is still possible and understanding super spreaders is the key, according to GP and mathematician David Kault.
In a paper to be published in the Medical Journal of Australia, Dr Kault, an adjunct senior lecturer at James Cook University, estimates the risk of lifting lockdown at various times near the end of the pandemic.
The paper argues that national elimination on an island continent can be achieved with a relatively short additional period of restrictions.
Dr Kault said Australia was at an elimination tipping point.
“It’s probably 50/50 at the moment as to whether we can eliminate COVID-19. A major factor is luck – luck as to whether someone is a super spreader or not,” he said.
Dr Kault said if a lockdown was lifted when numbers were low, but not zero, the situation became very brittle.
“Chance effects could lead to elimination or could lead to a second wave,” he said.
“Super spreaders are the key. We know there are occasional super spreaders who pass the disease on to many others, which means there are also people who pass the disease on to no one.”
The challenge is that the liability of an infected person to spread the disease varies considerably.
“The majority of infectious people don’t spread it to others,” Dr Kault said.
“And just 20 per cent account for 90 per cent of all subsequent infections.”
Towards the end of an epidemic, when communities have been locked down and only have a few cases, those few remaining cases may or may not be super spreaders.
Dr Kault said that was why leaving it to chance was too risky.
“According to probability theory, if numbers are low enough, the longer we go locked down the more surety we have of elimination, even allowing for super spreaders,” he said.
“As long as some community transmission remains, the possibility remains that there could be a super spreader who passes the disease on to several other super spreaders and control will be lost.”
Dr Kault said a policy of suppression without elimination led to an eventual increase in infections, which is happening in NSW and Victoria.
“We are seeing the consequences of opening up too soon,” he said.
“We can still eliminate but we need to lock down again now. We can’t get complacent because numbers are low. Mathematically, going the extra mile to lock down for a few extra weeks is worth it.”