October 8, 1999
Contact: CDC, Division of Media Relations
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Flu Season 1999-2000

Flu Pandemics

• There are two main types of influenza viruses, A and B. Type A viruses can be subtyped based on the surface protein hemagglutinin and neuraminidase. Influenza viruses can further be subdivided into strains. Currently, two strains of circulating influenza A subtypes affect people: H1N1 and H3N2. Pandemics result from the emergence, by antigenic shift, of an influenza A virus that people have not been exposed to and, therefore, do not have protective immunity against. However, in order for a new influenza virus to have the potential of becoming a pandemic, it must also be easily transmitted from person-to-person.
• Influenza viruses undergo two kinds of change. One is a series of mutations over time that cause a gradual evolution of the virus, known as drift which results in the emergence of new strains. The other is an abrupt change in the surface proteins, known as antigenic shift which results in new subtypes of influenza A.
• Flu pandemics have been recognized since the 1500s. During this century, pandemics occurred in 1918, 1957, and 1968. Birds are the primary reservoir for new influenza viruses. All 15 recognized influenza A subtypes have been found in birds.
• Although death rates associated with the recent pandemics of 1957 and 1968 were confined primarily to the elderly and chronically ill, both pandemics were associated with high rates of illness and social disruption, with combined economic losses of approximately $32 billion (in 1995 dollars).
• In most years in the United States, influenza-related complications are responsible for 10,000-40,000 deaths, 50,000-300,000 hospitalizations, and approximately $1-3 billion in direct costs for medical care.
• The impact of the next pandemic could have a devastating effect on the health and well being of the American public. CDC estimates that in the United States alone:
• Up to 200 million persons may be infected;
• Between 40 and 100 million persons may become clinically ill;
• Between 18 and 45 million persons may require outpatient care;
• Between 300,000 and 800,000 persons may be hospitalized
• Between 88,000 and 300,000 persons may die.
• Federal experts in public health and vaccine development are working to reduce the impact of flu each year, as well as helping to coordinate national preparations for the eventuality of a flu pandemic or outbreak of a new influenza strain. Researchers at CDC, the National Institutes of Health, and the Food and Drug Administration work together to identify new strains of influenza and develop annual vaccines. In addition to the United States, flu pandemic planning includes representatives from the World Health Organization, and ministries or departments of health from a number of other countries.
• On-going strategies to plan for the next flu pandemic include:
• Enhancing early detection capabilities;
• Improving readiness and decreasing the time required to mount a response to a pandemic;
• Identifying important gaps in existing research and prioritizing research efforts;
• Creating and institutionalizing protocols for decision-making and emergency management in the event of a pandemic;
• Identifying necessary resources for implementing a federal response in the event of a pandemic;
• Developing a flexible contingency plan for insuring availability of vaccines and antiviral agents in the event of a pandemic;
• Assisting state and local officials in developing state and local preparedness plans;
• Collaborating with the international community on pandemic preparedness planning;
• Enhancing pandemic influenza surveillance as part of CDC's emerging infections surveillance efforts.

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