A federal judge in Massachusetts on Monday blocked Health Secretary Robert F. Kennedy Jr.'s recent changes to the nation's childhood vaccine schedule, dealing a setback to the Trump administration's efforts to reshape federal vaccine policy.

The court ruling temporarily halted Kennedy's overhaul of childhood vaccination recommendations that had been developed by his allies within the Department of Health and Human Services. The changes represented a significant departure from established CDC vaccine guidance.

Kennedy, a longtime vaccine skeptic who was appointed to lead HHS, has made reforming vaccine policy a central focus of his tenure. His efforts have included revising vaccination schedules and making changes to advisory boards that oversee vaccine recommendations.

The judge's decision blocks not only the revised vaccine schedule but also other elements of Kennedy's vaccine agenda, including modifications to advisory committees involved in vaccine policy development. The ruling represents a major obstacle to Kennedy's broader plans to reshape how the federal government approaches childhood immunizations.

The legal challenge comes as Kennedy has moved quickly to implement policy changes since taking office, drawing both support from vaccine skeptics and criticism from public health advocates who argue that established vaccination schedules are based on extensive scientific research and safety data.