FILE - A syringe is prepared with the Pfizer COVID-19 vaccine at a vaccination clinic at the Keystone First Wellness Center in Chester, Pa., Dec. 15, 2021. Pfizer says tweaking its COVID-19 vaccine to better target the omicron variant is safe and boosts protection. Saturday, June 25, 2022 announcement comes just days before regulators debate whether to offer Americans updated booster shots this fall. (AP Photo/Matt Rourke, File)
FILE - A vial of the Moderna COVID-19 vaccine is displayed on a counter at a pharmacy in Portland, Ore. on Dec. 27, 2021. U.S. health authorities are facing a critical decision: whether to offer COVID-19 booster shots this fall that better match the omicron variant even though the coronavirus already has spawned still more mutants. Moderna and Pfizer are testing updated booster candidates, and advisers to the U.S. Food and Drug Administration will debate Tuesday, June 28, 2022, if it’s time for a switch, setting the stage for similar moves by other countries. (AP Photo/Jenny Kane, File)
U.S. health authorities are facing a critical decision: whether to offer new COVID-19 booster shots this fall that are modified to better match recent changes of the shape-shifting coronavirus.