While Kennedy insists he is not anti-vaccine and claims he has never advised the public to avoid vaccination, he has repeatedly expressed opposition to vaccines. On a podcast, he stated, "There's no vaccine that is safe and effective" and has urged people to resist CDC guidelines on childhood vaccination schedules.

The nearly $2 trillion agency administers health-insurance programs for millions of Americans, approves medications and oversees vaccine safety.

The choice will roil many public health experts after his years of touting debunked claims that vaccines cause autism.