Here’s the quick summary of the 2008 Report of the Commission on the Prevention of WMD Proliferation and Terrorism (PDF of full report):

RECOMMENDATION 1: The United States should undertake a series of mutually reinforcing domestic measures to … enhance the nation’s capabilities for rapid response to prevent biological attacks from inflicting mass casualties.

See also a National Pandemic Strategy document published by the Homeland Security Council in 2006: Implementation Plan for Pandemic Influenza

Three human influenza pandemics occurred in the 20th century, each resulting in illness in approximately 30 percent of the world population and death in 0.2 percent to 2 percent of those infected. Using this historical information and current models of disease transmission, it is projected a modern pandemic could lead to the deaths of 200,000 to 2 million U.S. citizens.