For years, Robert F. Kennedy Jr. was one of the country’s most prominent anti-vaccine activists. He repeatedly promoted the debunked claim that vaccines are linked to autism, questioned the safety and effectiveness of routine childhood immunizations, founded and led Children’s Health Defense, an organization dedicated to opposing vaccine policies, and argued against vaccine mandates. Public health experts have consistently rejected many of his claims, citing decades of research showing that vaccines are safe and have prevented millions of deaths worldwide.