By Michael Erman and Manojna Maddipatla (Reuters) -The U.S. Food and Drug Administration on Tuesday authorized a second booster dose for people age 50 and older of the two most commonly used COVID-19 vaccines, citing data showing waning immunity and the risks posed by Omicron variants of the virus. The agency said the new boosters – a fourth round of shots for most vaccine recipients – of the Pfizer Inc/BioNTech SE and Moderna Inc vaccines are to be administered at least four months after the previous dose. They are intended to offer more protection against severe disease and hospitalization. …