Small children often seem to be petri dishes of disease, rocking a perpetually runny nose and in the grip of a seemingly endless string of colds that they pass on to their classmates and family.
But as the pandemic played out this year, it became clear that this didn't really appear to be the case for COVID-19.
On Wednesday, when announcing changes to visitor numbers in Greater Sydney, NSW Premier Gladys Berejiklian said "children under 12 have been proven not to be carriers or transmitters of the disease".
A NSW Health spokesperson clarified that "children under 12 are not included in visitor numbers as they are generally less likely to transmit the virus that causes COVID-19, both to other children and to adults outside their own households".
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While kids are certainly not immune to COVID-19, with a rare few going on to develop an inflammatory condition associated with the virus, they're generally not a major source of disease spread — even to people they live with.
In a paper published earlier this month, University of Queensland virologist Kirsty Short and colleagues examined COVID-19 transmission in households to determine if an adult or a child introduced the disease to the home.
"What we found across multiple countries at different times was that it was very, very rare for the child to be the one bringing the infection into the household," she said.
This is in stark contrast to, for instance, the H5N1 strain of influenza, where half the time, it's a child that brings it into the home.
Dr Short and her team also found that if someone in a household came down with COVID-19, children were significantly less likely to get infected than the adults they lived with.
Asha Bowen, a paediatric infectious diseases specialist at Telethon Kids Institute and Perth Children's Hospital, said Australian school data showed something similar.
"A lot of the time when there's a cluster linked to a school, it's linked to the broader school community — not necessarily the children in the classroom or even the staff at the school," she said.
"It's much more the interactions that occur with sport, cultural activities, family mixing and things like that, and that adults are probably predominant drivers of transmission."
So what's going on with kids and COVID-19?
The short answer is: we don't exactly know yet.
But there are likely loads of elements that contribute to a youngster's relative fortitude against COVID-19 infection and transmission, said Marc Pellegrini, an infectious diseases researcher at the Walter and Eliza Hall Institute.
There is some evidence that their lungs and nasal passages contain fewer ACE2 receptors, which are points of entry for the SARS-CoV-2 virus.
But as kids grow into adults, they produce more ACE2 — and, thus, more routes for the virus to infect the cells.
Their young and relatively inexperienced immune system may be helpful too, Professor Pellegrini said.
"Certainly a lot of the people that get severe disease seem to have an overzealous immune response, which is sort of counterintuitive and somewhat destructive."
This "cytokine storm" is rarely seen in children, he added, "perhaps because their immune system is much more immature".
Even if children become infected with SARS-CoV-2, they have fewer or less severe symptoms, Professor Pellegrini said.
"So they still might be able to transmit the virus, but because they're not getting severely sick, they don't have that massive cough that a lot of adults get, so they are less likely to be a vessel of transmission compared to adults."
Cross-protective immunity — that is, some level of protection from exposure to other coronaviruses kids encounter in the wild — may play a part too, Dr Short said.
Still, we might have more answers soon. Dr Short has as-yet unpublished data that suggests children's immune systems are fundamentally different to adults' in such a way that their immune response is better able to control the SARS-CoV-2 virus.
Dr Bowen said untangling how kids' bodies grapple with the coronavirus "will have important findings for the whole population, not just for children.
"There's something about children with this particular virus that is different and that we can learn from."
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2020-12-24 21:03:00Z
CBMib2h0dHBzOi8vd3d3LmFiYy5uZXQuYXUvbmV3cy9oZWFsdGgvMjAyMC0xMi0yNS9jaGlsZHJlbi1jb3ZpZC0xOS1jb3JvbmF2aXJ1cy1zcHJlYWQtdHJhbnNtaXNzaW9uLWltbXVuZS8xMzAxMjU1MNIBJ2h0dHBzOi8vYW1wLmFiYy5uZXQuYXUvYXJ0aWNsZS8xMzAxMjU1MA
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