"There are three key questions: How much do children get COVID-19; how badly does it affect them; and do they spread it to others? We only have good data about the second of these.
"We know that most children have few, if any, symptoms if they contract COVID-19, and very few become severely ill, although we don’t know how often children have asymptomatic disease.
"The data on susceptibility and transmission of COVID-19 by children are much more unclear. These data show that children can have viral loads which are as high as adults, which is reported to suggest they may transmit as much as in adults. However the histograms of viral load for age groups show few children in the higher load categories. They report a sub-analysis which suggests that children with underlying conditions have lower viral loads than healthy children, which is puzzling and may suggest issues with bias in terms of sampling, given the sampling does not appear to be population-based.
"Some contract tracing studies suggest that infection attack rates are similar in children to adults, although other data from population testing and household cluster studies suggests that children may be less susceptible than adults and there is little evidence of transmission in some studies.
"This lack of clarity on transmission produces uncertainty for planning to reopen schools. Both keeping schools closed and reopening them carry degrees of risk in terms of population harms. Further data on susceptibility and transmission from population-based studies is urgently needed."
An analysis of SARS-CoV-2 viral load by patient age’ by Jones et al is posted on the (PDF).