The research, a modeling study using data from 32 locations China, Italy, Japan, Singapore, Canada and South Korea, found that by contrast, COVID-19 symptoms appear in 69% of infections in people aged 70 or older.
The findings suggest that school closures – introduced in many countries as part of lockdowns aimed at controlling the coronavirus pandemic – are likely to have a limited impact on transmission of the disease, the researchers said.
Published in the journal Nature Medicine, the study compared the effect school closures on simulated outbreaks of flu – which is known to spread swiftly in children – and of COVID-19, the disease caused by the new coronavirus.
"For COVID-19, there was much less of an effect of school closures," said Rosalind Eggo, an infectious disease modeler at The London School of Hygiene and Tropical Medicine who co-led the study.
She added, however, that the findings come from simulated outbreaks and need to be reinforced with real-world research.
Using demographic data from the six countries, as well as from six studies on estimated COVID-19 infection rates and symptom severity across different age groups, the model showed that people under 20 are about half as susceptible to COVID-19 as people over 20, and that among 10 to 19 year-olds, only 21% of those infected had clinical symptoms.
The researchers also simulated COVID-19 epidemics in 146 capital cities around the world and found that the total expected number of clinical cases varied with median age."The age structure of a population can have a significant impact," said Nicholas Davies, who co-led the work. "Countries with more young people may experience a lower burden of COVID-19."