The director of the Centers for Disease Control and Prevention on Friday overruled a recommendation by an agency advisory panel that had refused to endorse booster shots of the Pfizer-BioNTech Covid vaccine for frontline workers. It was a highly unusual move for the director, Dr. Rochelle Walensky, but aligned C.D.C. policy with the Food and Drug Administration's endorsements over her own agency's advisers. The C.D.C.'s Advisory Committee on Immunization Practices on Thursday recommended the boosters for a wide range of Americans, including tens of millions of older adults and younger people at high risk for the disease. But they excluded health care workers, teachers and others whose jobs put them at risk. That put their recommendations at odds with the F.D.A.'s authorization of booster shots for all adults with a high occupational risk. Dr. Walensky's decision was a boost for President Biden's campaign to give a broad segment of Americans access to boosters. The White House had come under criticism for getting ahead of the regulatory process. Dr. Walensky's decision to go against her own agency's advisers came as a surprise to at least some of her staff members: The C.D.C. director's endorsement of the advisory committee's recommendations is typically just a formality. Hours before her statement, agency insiders predicted she would stick with the usual protocol because doing otherwise would undermine the process and upset the advisers as well as her own staff.