Children younger than five with COVID-19 carry a much higher viral load in their upper respiratory tracts than older children and adults, a small US study shows.

The findings on SARS-CoV-2 levels in three age groups affected by mild to moderate COVID-19 raise new questions about whether children can infect others, the researchers say.

Data on children as sources of coronavirus spread are sparse, and early reports have not found strong evidence of children as major contributors to the pandemic.

Understanding the transmission potential in children will be key to developing public health guidelines, say the authors from the Ann & Robert H. Lurie Children’s Hospital in Chicago in JAMA Pediatrics.