COVID-19 vaccinations for children under 5 hit another monthslong delay Friday as U.S. regulators abruptly put the brakes on their efforts to speed review of the shots that Pfizer is testing for youngsters. The FDA, worried about the omicron variant’s toll on kids, had taken the extraordinary step of urging Pfizer to apply for OK of the extra-low dose vaccine before it’s clear if tots will need two shots or three.