The crisis began with a patient in an Oklahoma City hospital complaining of fever, aches, and rashes. It turned out to be smallpox—a disease that had not been seen in the United States for more than three decades. By the end of one day, there were thirty-four confirmed or suspected cases of smallpox in Oklahoma, as well as nine in Georgia and seven in Pennsylvania—the apparent work of Iraqi or other terrorists who had released the smallpox virus at shopping malls in those three states. Oklahoma’s governor requested that all 3.5 million residents of his state be immediately vaccinated, but because of shortages of the smallpox vaccine, only 100,000 doses were initially provided.

By day six hospitals were overwhelmed with two thousand smallpox cases in fifteen states. Television cameras depicted angry...