Doubts over herd mentality on COVID-19

The controversial method has the backing of the Dutch government led by prime minister Mark Rutte, and has had the apparent support of the British government's chief scientific adviser. Experts in Australia have raised doubts.

They've also flagged the flow-on effects that would follow if schools were closed in a bid to stop COVID-19 from spreading.

Today we look at the idea of "herd immunity", and why closing schools isn't the straightforward measure it might seem.

"Herd immunity" refers to preventing an infectious illness from spreading by vaccinating a certain percentage of the population.

The idea is to have enough people immune to the illness that the chain of infection through the population (or "herd") is interrupted, stopping it from reaching those who are most vulnerable but can't be vaccinated.

If enough people are vaccinated and immune, those who aren't still receive protection.

The Dutch government aims to build COVID-19 immunity in its population by letting large numbers get the virus at a controlled pace, while the UK's chief science officer has previously said its government would aim to build up a "herd immunity".

Discussions of "herd immunity" are different when it comes to COVID-19, because it's not known what percentage of the population needs to be immune to protect people who are vulnerable.

Right now, it's being suggested between 70 and more than 80 per cent of people could need immunity from COVID-19 to protect the rest of the community.

Medical experts are still uncertain whether coronavirus infection creates immunity, or how long that immunity might last. There's no vaccine, so there's no option to build immunity in the population without people developing the illness and therefore the possibility of severe consequences.

Researchers are still learning about COVID-19 and its behaviour.

La Trobe University epidemiologist Hassan Vally said it was a very risky strategy to allow a disease that was known to have severe outcomes to run its course in a large group of the population in order to develop "herd immunity" and, in theory, protect more vulnerable groups.

"By doing this you are in fact putting many people at risk of severe illness," Associate Professor Vally said.

The head of the Garvan Institute of Medical Research's inflammatory diseases lab, Professor Stuart Tangye, has also spoken against the idea.

"We do not know what the level of herd immunity that is going to be required to protect the broader community against COVID-19.

"Until this is known and until immunity is elicited more broadly by a vaccine, relying on herd immunity to prevent or slow down this pandemic is not a good strategy."

The ACT government has said it is focused at the moment on a "localised response" should there be a case at a school, and that any further decisions on schools would be made at a national level.

ACT Chief Minister Andrew Barr has said the matter of closing schools was one that would have a nationally-consistent approach, and pointed to the flow-on effects it would have.

"Once they are closed, they will be very difficult to reopen, that's a pretty fundamental point to make, and it has such significant implications," he said on Monday.

Associate Professor Vally said school closures could have unintended consequences.

"If all children were to be kept away from school there would be consequences for children in missing out on classes and for parents in having to organise care of their children and who may have to take time off work," he said.

"This includes parents who are healthcare workers and would not be able to go to work at this important time.

"The call seems to have been made at this stage of the epidemic in Australia that the amount of community transmission we have does not justify this action, but you can be assured that this decision will be revisited as we see how the epidemic progresses in Australia."

Doherty Institute research fellow Dr Trish Campbell said children at home may have closer contact with COVID-19 pathogens than at a school implementing social distancing measures like increasing spaces between desks.

"If at home, children may need to be looked after by grandparents, who are more vulnerable to serious disease," she said.

"If at some stage Australia does go down the path of school closures, it will be important to ensure that children are in an environment with appropriate social distancing."

There's even doubt that closing schools would do much to slow the spread of coronavirus.

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University of Queensland microbiology professor Ian Henderson said the experience from the Spanish flu pandemic did not indicate there were significant benefits from closing schools.

"Given the longevity of the incubation period for coronavirus it may only have a marginal impact of flattening the curve," he said.

Even if children weren't going to school for 13 weeks, it was likely they would still mix, transmitting the virus if they had it, Professor Henderson said.

"The flow-on impact to the economy and healthcare system could be significant," he said.

"The answer is not always 'do it now'."

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