WASHINGTON: US manufacturer Moderna on Tuesday said it has started Covid-19 vaccine trials for children aged from 6 months to under 12 years old, with plans to enroll about 6,750 participants. "We are pleased to begin this Phase 2/3 study of mRNA-1273 in healthy children in the US and Canada," said CEO Stephane Bancel in a statement. "This pediatric study will help us assess the potential safety and immunogenicity of our Covid-19 vaccine candidate in this important younger age population."