adolescents between 12 and 18 years old. US manufacturer Moderna has begun studying its coronavirus vaccine in children aged six months to 12 years old as the company informed that it plans to enroll children in the US and Canada for the trial. Watch: "We are pleased to begin this Phase 2/3 study of mRNA-1273 in healthy children in the US and Canada," Moderna CEO Stephane Bancel said. Moderna's testing comes even as schools across the US are under pressure to reopen fully amid surging coronavirus infections in the country. At least 17.8 million adults have received the Moderna vaccine in the United States, according to the company.