FILE - Licensed practical nurse Yokasta Castro, of Warwick, R.I., draws a Moderna COVID-19 vaccine into a syringe at a mass vaccination clinic, May 19, 2021, at Gillette Stadium, in Foxborough, Mass. While all eyes are on the new and little-understood omicron variant, the delta form of the coronavirus isn't finished wreaking havoc in the U.S. There is much that is unknown about omicron, including whether it is more contagious than previous versions, makes people sicker or more easily thwarts the vaccine or breaks through the immunity that people get from a bout of COVID-19. (AP Photo/Steven Senne, File)