In the wake of 11 September 2001, many public health agencies are reassessing their institutional capabilities and procedures to respond to mass-casualty incidents involving weapons of mass destruction. Prior to the fall of 2001, planning by the public health and other sectors addressed more conventional or naturally occurring events such as earthquakes, hurricanes, tornados, and chemical spills, although attacks with weapons of mass destruction were a growing concern. While the nature of natural versus intentional events differs, the management and coordination of response activities to them follows the same incident command system.

A major lesson learned during the response operations to the 11 September 2001 attacks in New York City was the value of disaster planning, conducting exercises, and developing relationships among the various response agencies. Although New York City's physical Emergency Operations Center (EOC) at 7 World Trade Center was destroyed in the attack, the medical and health response community was able to react effectively to the possibility of mass casualties as well as to the more usual needs. This was enabled by the pre-existing relationships that had been developed between city, state, federal, and non-governmental agencies while planning and exercising for such events and their aftermaths.