The companies studied a 10 microgram vaccine dose in children 5 to 11, a third of the dose used for adults and older children. The lower dose was chosen to minimize side effects and because it still prompts a strong immune response, the companies said.

In the main clinical trial conducted by the companies, the vaccine appeared to be more than 90% effective against symptomatic COVID-19

No new safety problems were identified in the companies’ studies. No cases of heart inflammation were observed in the main study, but only a few thousand children were included in the research so that sort of rare problem wouldn’t necessarily be detected.