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)

FILE - Men are seated after receiving the a third Pfizer-BioNTech COVID-19 vaccine at a coronavirus vaccination center in Tel Aviv, Israel, Tuesday, Aug. 10, 2021. The coronavirus's omicron variant kept a jittery world off-kilter Wednesday Dec. 1, 2021, as reports of infections linked to the mutant strain cropped up in more parts of the globe, and one official said that the wait for more information on its dangers felt like “an eternity.” (AP Photo/Oded Balilty, File)