Under the Tenth Amendment, the core police power over public health -- vaccination requirements, isolation, school mandates, licensing of medical professionals -- belongs to the states. The federal government enters through interstate commerce, the spending clause (Medicaid and federal grants), and explicit statutes like the Public Health Service Act that give CDC quarantine authority at borders and between states.
In day-to-day practice the two layers cooperate: CDC produces national recommendations, states adopt them by statute or rule, and federal funding flows through to state and local health departments. When federal recommendations break down -- as after HHS Secretary Kennedy purged ACIP in June 2025 -- states can chart their own course. California, New York, and others signaled in 2025 they would follow American Academy of Pediatrics guidance over CDC, and state attorneys general considered litigation to preserve insurance coverage for vaccines CDC dropped.
The federalism split limits federal damage but also limits federal protection: a state that rejects vaccination requirements cannot be forced to adopt them, and citizens may face very different public health regimes depending on where they live.
When federal public health falters, the states become the firewall -- and the only one. Understanding which decisions sit at which layer tells citizens where to direct pressure when something breaks at the top.
People often think federal recommendations bind states. They do not -- states adopt them voluntarily, and can diverge whenever a governor and legislature choose.
When federal public health falters, the states become the firewall -- and the only one. Understanding which decisions sit at which layer tells citizens where to direct pressure when something breaks at the top.
People often think federal recommendations bind states. They do not -- states adopt them voluntarily, and can diverge whenever a governor and legislature choose.