The pharmaceutical industry has a “complex and mutually-dependent” relationship with physician trade groups and physicians. Although the details are not always fully or accurately documented, the funding trail can often provide revealing clues. Thus, the American Academy of Pediatrics (AAP), one of the most notorious vaccine industry front groups, receives funding from all four manufacturers of childhood vaccines in the U.S. (Merck, Pfizer, Sanofi, GlaxoSmithKline).