Doctors are starting to think children don't appear to be as affected by COVID-19 as adults are thanks to their healthy blood vessels.
Children are less likely than adults to show symptoms of having the mysterious illness, and when they do fall sick, are far less likely to die.
Most viral illnesses affect the young and elderly the most, but COVID-19 overwhelmingly targets the elderly - just why it leaves children mostly alone has been a mystery until now.
Researchers in Switzerland think it could be their blood vessels, which haven't been ravaged by time.
SARS-CoV-2, the virus which causes COVID-19, can infect endothelial cells, the scientists found. Endothelium lines blood vessels and prevents clotting.
Blood clots have been found in many patients that have lost their lives to the respiratory disease.
"A kid's endothelium is set up perfectly and then just deteriorates with age," Paul Monagle, a paediatric haematologist at the Melbourne Children's Campus, told Nature.
"If we understand what happens to children, we could tweak adults to make them more child-like."
Only 10 percent of New Zealand's cases of COVID-19 were in people aged under 20, and only 2 percent in people under 10, a Ministry of Health document from early May said.
This is actually higher than most other countries, thanks to our small total case count including "COVID-19 clusters that involve school-aged children".
Few children who fall ill with the disease have clotting and damaged blood vessels.
The finding could also explain why people with other conditions that affect endothelium - such as diabetes and hypertension - seem to be at greater risk of complications from COVID-19.
