Federal quarantine orders, however, are implemented and enforced by state health authorities, not federal officials. That means state and local health departments provide the labor, set the rules, monitor people who might have been exposed to the virus, and trace the contacts of those who fall ill. The federal quarantine order for the 195 evacuees from Wuhan? That order was able to prevent them from leaving the plane they arrived in. The federal government could also order the quarantine of an entire cruise ship at one of the nation’s seaports—as Japan has done. But otherwise, federal quarantine orders have a pretty limited effect. When one of the Wuhan evacuees wanted to leave the military base in California where the group was under quarantine, a state-level quarantine order was necessary to prevent that from happening. This is because the quarantined group was no longer at a point of entry, or in an airplane, and was thus subject to the jurisdiction of the local health department where they were quarantined.
Despite extensive federal measures to protect the U.S. from threats originating abroad, inevitably a virus will get through screening (as indeed the Wuhan coronavirus already has). This is where the weakness of a federalist system of national health defense is exposed. States may choose to ignore federal quarantine guidelines, or they may decide that more drastic measures are required, such as a lockdown against a neighboring city or region. Extreme measures may be necessary in a public-health emergency, but the variation from one location to another could also make an epidemic worse as each state makes its own rules, looks out for its own interests, and relies on its own resources. Jurisdictional boundaries are enforced, among other reasons, to preserve limited budgets.
This unique brand of public-health federalism can make implementing a national strategy in the event of a threatened epidemic very difficult.