Vaccine shortages and distribution problems during the 2004-2005 influenza season raised concerns about the nation's ability to respond to a worldwide influenza epidemic--or influenza pandemic--which many experts believe to be inevitable. Some experts believe that the next pandemic could be spawned by the recurring avian influenza in Asia. If avian influenza strains directly infect humans and acquire the ability to be readily transmitted between people, a pandemic could occur. Modeling studies suggest that its effect in the United States could be severe, with one estimate from the Centers for Disease Control and Prevention (CDC) ranging from 89,000 to 207,000 deaths and from 38 million to 89 million illnesses. GAO was asked to discuss surveillance systems in place to identify and monitor an influenza pandemic and concerns about preparedness for and response to an influenza pandemic. This testimony is based on GAO's 2004 report on disease surveillance; reports and testimony on influenza outbreaks, influenza vaccine supply, and pandemic planning that GAO has issued since October 2000; and work GAO has done in May 2005 to update key information.