Influenza is characterized by cough, fever, headache, and other symptoms and is more severe than some viral respiratory infections, such as the common cold. Most people who contract influenza recover completely in 1 to 2 weeks, but some develop serious and potentially life-threatening medical complications, such as pneumonia. On average each year in the United States, more than 36,000 individuals die and more than 200,000 are hospitalized from influenza and related complications. People aged 65 years and older, people of any age with chronic medical conditions, children younger than 2 years of age, and pregnant women are generally more likely than others to develop severe influenza-related complications. Vaccination is the primary method for preventing influenza and its more severe complications. Produced in a complex process that involves growing viruses in millions of fertilized chicken eggs, influenza vaccine is administered annually to provide protection against particular influenza strains expected to be prevalent that year. Experience has shown that vaccine production generally takes 6 or more months after a virus strain has been identified, and vaccines for certain influenza strains have been difficult to mass-produce. After vaccination, the body takes about 2 weeks to produce the antibodies that protect against infection. According to CDC, the optimal time for vaccination is October through November, because the annual influenza season typically does not peak until January or February. Thus in most years, vaccination in December or later can still be beneficial (see fig. 1). If supplies permit, CDC recommends a vaccination for anyone who wants one. Because circulating influenza strains change, a new vaccine is created each year. For this reason, and because immunity declines over time, CDC recommends a new influenza vaccination every year for high-risk individuals and other priority groups, including close contacts of those at high risk. Two types of vaccine are recommended for protection against influenza in the United States: (1) an inactivated virus vaccine injected into muscle and (2) a live virus vaccine administered as a nasal spray. The injectable vaccine—which represents the large majority (over 95 percent) of influenza vaccine administered in this country—can be used to immunize healthy individuals and those at high risk of severe complications, including those with chronic illness and those aged 65 years and older. The nasal spray vaccine, in contrast, is currently approved for use only among healthy individuals aged 5–49 years who are not pregnant. Although vaccination is the primary strategy for protecting individuals who are at greatest risk of serious complications and death from influenza, antiviral drugs can also contribute to the treatment and prevention of the disease. In a typical year, manufacturers make influenza vaccine available before the optimal fall vaccination season. For the 2003–04 influenza season, two manufacturers—one with production facilities in the United States (sanofi pasteur) and one with production facilities in the United Kingdom (Chiron)—produced about 83 million doses of injectable vaccine, which represented about 96 percent of the U.S. vaccine supply. A third U.S. manufacturer (MedImmune) produced the nasal spray vaccine. According to CDC, MedImmune produced about 3 million doses of the nasal spray vaccine, or about 4 percent of the overall influenza vaccine supply, for the 2003–04 season. Influenza vaccine production and distribution are largely private-sector activities. Manufacturers sell influenza vaccine to resellers (such as medical supply distributors and pharmacies), to federal agencies and state and local public health departments, or directly to providers (see fig. 2). Individuals can obtain an influenza vaccination at a number of places, including physicians’ offices, public health clinics, nursing homes, and nonmedical locations such as workplaces or retail outlets. Millions of individuals receive influenza vaccinations through mass immunization campaigns in these nonmedical settings, where organizations such as visiting nurse agencies under contract administer the vaccine. HHS has limited authority to control vaccine production and distribution directly; influenza vaccine supply and marketing are largely in the hands of the private sector. In the event that the Secretary of HHS determines and declares a public health emergency, the Public Health Service Act authorizes the Secretary to “take such action as may be appropriate” to respond. Within HHS, CDC is one of the agencies that help protect the nation’s health and safety. CDC’s activities include efforts to prevent and control diseases and to respond to public health emergencies. ACIP, after consulting with CDC, makes recommendations on which population groups should be targeted for vaccination. CDC also administers a number of programs to help make vaccines, including influenza vaccine, affordable for low-income and other populations. For example, under CDC’s Vaccines for Children program, vaccines are provided free of charge for certain children 18 years of age or younger, including those who are Medicaid- eligible, uninsured, or underinsured (that is, their insurance does not include vaccinations). CDC also reserves stockpiles of certain vaccines. For the 2004–05 influenza season, CDC contracted with vaccine manufacturers to supply influenza vaccine for a national stockpile for the first time. The agency originally contracted for 4.5 million doses, including 2 million doses from Chiron, which were therefore not available. CDC also maintains stockpiles of antiviral medications that can alleviate influenza symptoms and reduce contagion in those who contract the disease. Other organizations within HHS that are involved with immunization activities include the National Vaccine Program Office, which is responsible for coordinating and ensuring collaboration among the many federal agencies involved in vaccine and immunization activities, and the Food and Drug Administration (FDA), which in approving and regulating the use of vaccines and drugs, including antiviral medications, is responsible for ensuring that they are safe and effective. In addition to federal agencies, state and local health departments are often the first responders in situations affecting public health. Initially for the 2004–05 influenza season, CDC in May 2004 recommended that about 188 million Americans receive a vaccination—about 85 million at high risk of severe complications and about 103 million in other priority groups, such as people in close contact with high-risk individuals, healthy people aged 50–64 years, and health care workers. CDC also suggested that, depending on the availability of vaccine, other individuals who should receive a vaccination include (1) any person who wished to reduce the likelihood of contracting influenza, (2) individuals who provide essential community services, and (3) students and others in institutional settings. Although Chiron had announced that it was experiencing production problems in August 2004, according to CDC, the manufacturer had assured the agency that the production issues were being resolved. Subsequently, on September 24, 2004, CDC reiterated its recommendation that 188 million individuals in high-risk and other groups be vaccinated as vaccine became available. CDC also recommended that anyone wanting to reduce the risk of contracting influenza be vaccinated. Not everyone in these high-risk and priority groups, however, receives a vaccination each year. Among health care workers, for example, about 40 percent received a vaccination in the 2002–03 and 2003–04 seasons, according to one CDC survey. Similarly, about 66 percent of individuals aged 65 years and older reported receiving influenza vaccination in the 2002–03 and 2003–04 influenza seasons, according to CDC estimates. After the October 5, 2004, announcement of the sharp reduction in expected influenza vaccine supply, federal, state, and local health officials took steps to help ensure that those at high risk of severe complications from infection had access to influenza vaccine. For example, health officials quickly revised vaccination recommendations so that the remaining supply could be targeted to those in priority groups comprising those at high risk, certain health care workers, and household contacts of children younger than 6 months of age. Other efforts focused on distributing vaccine to priority groups and on keeping providers and the public updated as to vaccine availability. Finally, late in the influenza vaccination period—from mid-December through January—health officials’ actions focused on further augmenting the vaccine supply and, once supply increased, on encouraging vaccination for anyone remaining in the priority groups and for others who had earlier deferred vaccination (see fig. 3). Several responses by public health officials took place within hours or days of the public announcement that a severe shortage of influenza vaccine was imminent. Federal and state health officials redefined priority groups for influenza vaccination. CDC immediately redefined the groups recommended to receive vaccine in 2004–05 for protection against influenza and its complications and issued revised recommendations on October 5, 2004. These revised recommendations focused on priority groups that included high-risk individuals, health care workers involved in direct patient care, and household contacts of children younger than 6 months of age. CDC’s revised recommendations decreased the number of people in groups recommended for vaccination from about 188 million to about 98 million (see table 1). At the same time, CDC also asked people not in these priority groups to forgo or defer vaccination. State and local health officials we met with reported having quickly adopted CDC’s revised recommendations. Some health departments, however, found that they did not have enough vaccine to cover everyone in CDC’s priority groups and therefore subdivided CDC’s priority groups. For example, in Maine, all health care workers were initially excluded from the state’s priority groups, although later, Maine health officials recommended vaccination for particular types of health care workers, such as those working in intensive care units and emergency departments, if local vaccine supply allowed. HHS collaborated with manufacturers to temporarily halt further distribution of injectable influenza vaccine and to ramp up production of nasal spray vaccine. At the request of CDC, sanofi pasteur, the sole remaining manufacturer of injectable influenza vaccine for the U.S. market, voluntarily suspended further distribution of the approximately 25 million doses it had not yet shipped on October 5, 2004, until the week of October 11, 2004, when CDC completed its assessment of the situation. Distribution was temporarily halted because CDC needed time to devise a plan to better target vaccine distribution to providers serving individuals in the priority groups. HHS officials also worked with MedImmune, the maker of the nasal spray vaccine, to increase its production for the 2004–05 influenza season from about 1 million doses to a total of 3 million doses.