Pfizer has asked U.S. regulators to authorize its combination COVID-19 vaccine that adds protection against the newest omicron relatives. The move Monday is a key step toward opening a fall booster campaign. The Food and Drug Administration ordered vaccine makers to tweak their shots to target BA.4 and BA.5 that are better than ever at dodging immunity from earlier vaccination or infection. If the FDA quickly clears the combo shots made by Pfizer and its partner BioNTech, boosters could be offered within weeks. Moderna is expected to file a similar application soon.