A nurse prepares doses of the Pfizer vaccine during a COVID-19 vaccination event at Josephine's Southern Cooking in Chatham, Illinois, Dec. 30, 2021.Brian Cassella | Tribune News Service | Getty ImagesA new round of Covid vaccines is finally here in the U.S.The Centers for Disease Control and Prevention cleared single-strain shots from Pfizer and Moderna for all Americans six months and up on Tuesday, following approvals from the Food and Drug Administration on Monday. Those mRNA vaccines are designed to target a relatively new omicron subvariant called XBB.1.5. The...