Why Is COVID-19 Less Severe in Children?

Early in the COVID-19 epidemic, it became clear that children generally were less vulnerable than adults to severe illness. Speculation that the frequent upper respiratory infections of childhood might be protective has been supported by some study results. To test this theory further and begin to unravel the mechanisms, researchers studied nasal swabs collected biweekly during 2020–2021 from about 1100 U.S. children, adolescents, and adults in a previous study. The present study’s authors used standard clinical PCR to identify incident respiratory virus infections and quantitate viral loads, then examined a subset of samples for genetic correlates of antiviral protection.