U.S. drug regulators on March 29 announced they’ve granted emergency authorization for a second booster of the Pfizer and Moderna COVID-19 vaccines The Food and Drug Administration (FDA) is allowing a fourth dose of the jabs to all Americans aged 50 and above. In addition, Americans aged 12 above with weakened immune systems may get Pfizer’s second booster, and Americans over the age of 18 who are immunocompromised may get a second booster of Moderna’s jab. The clearance is for four months after the receipt of an initial booster shot. Based on the studies, the FDA has concluded a second booster “may be effective” and that the “known and potential benefits” outweigh the “known and potential risks” in the populations now authorized to get one, Jacqueline O’Shaughnessy, the FDA’s chief scientist, told Pfizer and Moderna executives in separate letters. The vaccines are built on messenger RNA technology and both are …