The four times less aerosol particles produced by primary school-aged children when breathing, speaking or singing compared with adults could help explain why they seem to be at lower risk of spreading Covid.
According to various studies, young children are less susceptible to catching Covid than adults, and, despite carrying a similar amount of virus in their noses and throats, seem to pass it on to fewer people.
One possibility is that the size and shape of their lungs and respiratory tracts means they emit fewer tiny airborne droplets called aerosols as they breathe and speak. If fewer aerosols are left in the air, other people are less likely to be exposed to these particles, which linger in the air in classrooms.
To investigate, Dr Mario Fleischer at University Medicine Berlin and colleagues recruited 16 healthy children aged eight to 10 and used a laser particle counter to measure how many aerosol-sized particles they emitted when breathing and speaking.
The results suggested that shouting produced the most particles, followed by singing, speaking and breathing. Particle emission rates and volumes for singing, speaking and breathing were four times lower for children than for adults.
Children emit the same particle rates and volumes as adults while singing, and they emit the same particle rates and volumes while breathing, according to Fleischer.
Adults and children produced the same amount of aerosols during shouting.
The results didn't suggest that attending schools or after-school clubs was safe.
The aerosol emission could be similar for different age groups, as the measurements for the shouting condition show.
The number of children and the design of indoor air quality were two factors that mattered, as well as further research, to inform any recommendations made to schools.
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