WASHINGTON — 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 Food and Drug Administration, 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. The agency’s plan could have allowed vaccinations to begin within weeks. But Friday, the FDA reversed course and said it had become clear the agency needed to wait for data on how well a third shot works for the youngest age group. Pfizer said in a statement that it expected the data by early April. FDA’s vaccine chief Dr. Peter Marks said he hoped parents would understand that the agency’s decision was part of its careful scientific review of the evidence Pfizer has submitted so far. That information “made us realize that we needed to see data from a third dose from the ongoing trial in order to make a determination,” Marks told reporters. “We take our responsibility for reviewing these vaccines very seriously because we’re parents as well.” The nation’s 18 million children under 5 make up the only age group not yet eligible for vaccination. Rachel Perera, the mother of an 8-month-old from Los Angeles, said Friday’s news felt “like the rug just got pulled out from under me.” After consulting with her pediatrician, Perera hoped a vaccine would be available this winter, or in early 2022 at the latest. The education policy researcher and her husband are caring for their child to avoid the unpredictability and risks of child care during a pandemic. But that means working on her dissertation for the Ph. D. she is pursuing when her child sleeps. On top of that, the daily calculations of risks, she says, have left her with “decision fatigue.” “I’m just tired, and it feels like ‘when is this going to end’?” Perera said. “It feels like people around us are moving on with their lives, and we’re being left behind.” — Agencies