U.S. vaccine manufacturers have privately warned federal officials that proposed changes under Health Secretary Robert F. Kennedy Jr.’s leadership—such as discouraging or banning certain adjuvants and breaking up combination childhood vaccines—could force multibillion‑dollar reformulations, disrupt supplies, and imperil coverage of routine pediatric immunizations. Industry sources told reporters the changes could require companies to redevelop core vaccines, an effort that can take a decade and cost over $1 billion per product. Policymakers’ moves might reduce availability of vaccines that protect against measles, mumps, rubella, tetanus, diphtheria, pertussis and polio, potentially reversing long‑established pediatric schedules. Manufacturers and public‑health experts caution that rapid ingredient or formulation shifts carry significant programmatic and safety implications and could create long lead times and gaps in protection if pursued without transitional strategies.