Washington: Pfizer and BioNTech said Tuesday they began submitting a formal request to US health regulators for emergency use of their Covid vaccine for children aged over six months and under five years. The request is currently for two doses of a three-microgram shot, which will give parents “the opportunity to begin a Covid-19 vaccination series for their children while awaiting potential authorization of a third dose,” Pfizer CEO Albert Bourla said in a statement.