Robert F. Kennedy Jr., a longtime vaccine skeptic, may influence U.S. vaccine regulation under Trump, potentially slowing approvals and spreading disinformation. Kennedy seeks more transparency and data on vaccines, but his actions could face backlash from the public, Congress, and the drug industry. The CDC's Advisory Committee on Immunization Practices, vulnerable to influence, could be stacked with skeptics, impacting vaccine recommendations and affordability. Kennedy's soft power, already discouraging vaccine use, may grow with a federal position.