Pfizer enrolled 144 children in the first phase of the trial. The next phase of the study aims to enroll up to 4,500 children at more than 90 clinical sites in the U.S., Finland, Poland and Spain, the company said. Children ages 5 to 11 will receive a 10 microgram dose level, while those under 5 and down to 6 months will receive a 3 microgram dose level. The shots will continue to be given on a two-dose schedule spaced 21 days apart. The U.S. Food and Drug Administration has given an emergency use authorization to Pfizer’s COVID-19 vaccine in...