Pfizer, on Tuesday said that it will start a large study to test its coronavirus vaccine in children below 12 and selected a dosing regime for the trial, news agency Reuters reported.The study will enroll as many as 4,500 children at over 90 clinical sites in the US, Finland, Poland and Spain, the American pharmaceutical company said.The EU's drug watchdog had already approved the Pfizer/BioNTech Covid-19 jab for 12- to 15-year-olds, the first vaccine to get the green light for children in the bloc.The Pfizer Covid-19 vaccine was "well-tolerated" in children and there were no "major concerns" in terms of side effects, the Amsterdam-based European Medicines Agency had informed.The vaccine has also been authorised for use in children as young.