Pfizer on Thursday said it submitted a request to U.S. drug regulators to expand the authorization for its COVID-19 vaccine to children between the ages of 5 and 11. The U.S.-based pharmaceutical company and its German partner BioNTech sent the request to the Food and Drug Administration (FDA) about a week after submitting data they said showed the vaccine triggered antibody responses in children in a Phase 2/3 clinical trial. Full results for the trial, which is run by the companies, have not yet been released. “With new cases in children in the U.S. continuing to be at a high level, this submission is an important step in our ongoing effort against COVID-19,” Pfizer said in a statement. Pfizer’s shot is already authorized for children aged 12 to 17 and approved for adults 18 and older, though the approved version isn’t yet available in the United States. Some experts and …