One of the Centers for Disease Control and Prevention’s top vaccine specialists has warned that Robert F. Kennedy Jr.’s anti-vax policies will cause “a lot of Americans to die” after resigning from the agency on Monday.

RFK Jr. ousted the entire vaccine advisory panel, prompting backlash from experts who warned his abrupt decisions and controversial appointments could endanger U.S. immunization efforts and increase preventable disease outbreaks.

The health secretary fired all the members of the Advisory Committee on Immunization Practices late on Monday.