To be prepared for major public health threats such as an influenza pandemic, public health agencies need several basic capabilities, including disease surveillance systems. Specifically, to detect cases of pandemic influenza, especially before they develop into widespread outbreaks, local, state, and federal public health officials as well as international organizations collect, analyze, and share information related to cases of the disease. When effective, surveillance can facilitate timely action to control outbreaks and promote informed allocation of resources to meet changing disease conditions. Influenza is more severe than some other viral respiratory infections, such as the common cold. Most people who get influenza recover completely in 1 to 2 weeks, but some develop serious and potentially life-threatening medical complications, such as pneumonia. People aged 65 and older, people of any age with chronic medical conditions, children younger than 2 years, and pregnant women are more likely than other people to develop severe complications from influenza. Influenza and pneumonia rank as the fifth leading cause of death among persons aged 65 and older. Influenza viruses undergo minor but continuous genetic changes from year to year. Almost every year, an influenza virus causes acute respiratory disease in epidemic proportions somewhere in the world. Vaccination is the primary method for preventing influenza and its more severe complications. Influenza vaccine is produced and administered annually to provide protection against particular influenza strains expected to be prevalent that year. Influenza vaccine takes several months to produce. Deciding which viral strains to include in the annual influenza vaccine depends on data collected from domestic and international surveillance systems that identify prevalent strains and characterize their effect on human health. FDA decides which strains to include in the vaccine and also licenses and regulates the manufacturers that produce the vaccine. HHS has limited authority, however, to directly control influenza vaccine production and distribution. FDA has approved four antiviral medications (amantadine, rimantadine, oseltamivir, and zanamivir) for prevention and treatment of influenza. However, influenza virus strains can become resistant to one or more of these drugs, and so they may not always be effective. In the United States, responsibility for disease surveillance is shared— involving health care providers; more than 3,000 local health departments, including county, city, and tribal health departments; 59 state and territorial health departments; more than 180,000 public and private laboratories; and public health officials from multiple federal departments and agencies. States, through the use of their state and local health departments, have principal responsibility for protecting the public’s health and therefore take the lead in conducting disease surveillance and supporting response efforts. According to the Institute of Medicine (IOM), most states require health care providers to report any unusual illnesses or deaths—especially those for which a cause cannot be readily established. Generally, local health departments are responsible for conducting initial investigations into reports of infectious diseases. Laboratory personnel test clinical and environmental samples for possible exposures and identification of illnesses. Epidemiologists in health departments use disease surveillance systems to detect clusters of suspicious symptoms or diseases in order to facilitate early detection and treatment. Local and state health departments monitor disease trends. Local health departments are also responsible for sharing information they obtain from providers or other sources with their state departments of health. State health departments are responsible for collecting surveillance information—which they share on a voluntary basis with CDC and others—from across their state and for coordinating investigations and response efforts. Public health officials provide needed information to the clinical community and the public. At the federal level, several departments and agencies are involved in disease surveillance and response. For example, HHS has primary responsibility for coordinating the nation’s response to public health emergencies. As part of its mission, the department has a role in planning to prepare for and respond to an influenza pandemic. One action the department has taken is the development of a draft national pandemic influenza plan, titled “Pandemic Influenza Preparedness and Response Plan.” CDC is charged with protecting the nation’s public health by directing efforts to prevent and control diseases and responding to public health emergencies. It has primary responsibility for conducting national disease surveillance and developing epidemiological and laboratory tools to enhance disease surveillance. CDC also provides an array of technical and financial support for state infectious disease surveillance efforts. In addition, CDC participates in international disease and laboratory surveillance sponsored by WHO. FDA is responsible for ensuring that new vaccines and drugs are safe and effective and for conducting research on diagnostic tools and treatment of disease outbreaks. The agency also regulates and licenses vaccines and antiviral agents through the Center for Biologics Evaluation and Research and the Center for Drug Evaluation and Research, respectively. FDA also develops influenza viral reference strains and reagents and makes them available to manufacturers for vaccine development and evaluation. The Department of Defense (DOD) contributes to global disease surveillance, training, research, and response to emerging infectious disease threats. DOD maintains the DOD Influenza Surveillance Program, a laboratory-based surveillance program. DOD maintains multiple sites throughout the world that serve as sentinels for disease outbreaks, where it collects and analyzes viral specimens. The Department of Agriculture (USDA) is responsible for protecting and improving the health and marketability of animals and animal products by preventing, controlling, and eliminating animal diseases. USDA undertakes disease surveillance and response activities to protect U.S. livestock, ensure the safety of international trade, and contribute to the national zoonotic disease surveillance effort. The United States is a member of WHO, which is responsible for coordinating international disease surveillance and response efforts. An agency of the United Nations, WHO administers the International Health Regulations, which outline WHO’s role and the responsibility of member countries and regions in preventing the global spread of infectious diseases. WHO also helps marshal resources from its members to control outbreaks within individual countries or regions. In addition, WHO works with national governments to improve their surveillance capacities through—for example—assessing and redesigning national surveillance strategies, offering training in epidemiologic and laboratory techniques, and emphasizing more efficient communication systems. Surveillance is a key component in planning for an influenza pandemic, and federal public health officials plan to rely on the nation’s existing annual influenza surveillance system and enhancements to identify an influenza pandemic. Federal public health officials have undertaken several initiatives that are intended to enhance influenza surveillance capabilities. These initiatives have been undertaken both through programs specific to influenza as well as through programs focused more generally on increasing preparedness for bioterrorism and other emerging infectious disease health threats. Federal officials have implemented and expanded syndromic surveillance systems in order to detect outbreaks more quickly, but there are concerns that these systems are costly to run and still largely untested. Federal officials have also implemented initiatives designed to improve public health communications and have undertaken initiatives intended to improve the coordination of zoonotic surveillance efforts. Current U.S. surveillance for identifying annual influenza outbreaks as well as an influenza pandemic involves multiple public health partners at all levels of government and relies on several data sources. At the federal level, CDC’s Influenza Branch leads the national influenza surveillance effort, monitoring disease and viral trends using data submitted each week from October through May. These surveillance data are collected at the local and state levels and voluntarily submitted to CDC. Data submitted on influenza activity in the United States include data from more than 120 laboratories and 2,000 health care providers and mortality reports from 122 cities. In addition, influenza data are collected from all 50 state health departments and the health departments in the District of Columbia and New York City. CDC also receives data that are specifically focused on influenza in pediatric patients. When the data are used collectively, they provide a national picture of influenza activity. Specifically, they allow CDC to (1) identify when and where influenza activity is occurring, (2) determine what strains of the influenza virus are in circulation, (3) detect changes in the influenza virus, (4) monitor influenza-related illnesses, and (5) measure the impact influenza is having on deaths in the United States. DOD also plays a role in national and international influenza surveillance. Specifically, DOD’s Influenza Surveillance Program, under the direction of the Air Force, collects viral specimens from its active duty personnel and their dependents at military facilities around the world. DOD’s program also sends specimens to CDC for further analysis and contributes to the determination of which viral strains FDA includes in the nation’s annual influenza vaccine. Internationally, DOD provides viral specimens to WHO and assists in identifying emerging influenza strains. In countries throughout the world, infectious disease surveillance is a national responsibility, but WHO assists its members’ efforts through its Global Influenza Surveillance Network. WHO’s Network is composed of 112 institutions, called National Influenza Centres, from 83 countries. Collectively, these Centres monitor influenza activity and annually gather more than 175,000 viral specimens for analysis from patients with influenza-like illnesses throughout the world. Selected influenza isolates— an estimated 2,000 viruses—may also be sent to one of four WHO Collaborating Centres for further, more specific genetic analysis. The additional analysis conducted by the WHO Collaborating Centers is used for the annual WHO recommendations on which strains to include in the influenza vaccine for the northern and southern hemispheres. In addition to making recommendations on the components of the influenza vaccine, this Global Influenza Surveillance Network also serves as a global alert mechanism for the emergence of influenza viruses with pandemic potential. CDC has undertaken several initiatives that are intended to enhance influenza surveillance capabilities in preparation for an influenza pandemic. CDC works with its international partners to improve global surveillance for influenza. For example, CDC participates in international disease and laboratory surveillance sponsored by WHO. Also, when concerns were raised over recent influenza seasons that the avian influenza A (H5N1) could become the next influenza pandemic, CDC led a variety of efforts with its international partners to plan for and address threats of increased influenza activity worldwide. For example, CDC worked collaboratively with WHO to conduct investigations of avian influenza A in Vietnam and to provide laboratory testing. CDC also provided training assistance and has implemented an initiative to improve influenza surveillance in Asia.