Aaron Siri, a lawyer advising Robert F. Kennedy Jr. as he prepared to become health secretary, petitioned the Food and Drug Administration in 2022 to revoke approval of a polio vaccine that is used widely in the U.

Robert F. Kennedy Jr. worked strenuously Wednesday to clarify his views on vaccines after a top Democrat challenged him on past statements and actions that seemed to suggest he was a blanket opponent of shots.

Sen. Bill Cassidy, the top Republican on the Senate Committee on Health, Education, Labor and Pensions, concluded Thursday's hearing by saying he was "struggling" with the nomination due to Kennedy's vaccine positions. Kennedy notably refused to say vaccines don't cause autism as he faced pointed question from lawmakers.