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Introduction In the United States, annual epidemics of influenza occur typically during the late fall and winter seasons; an annual average of approximately 36,000 deaths during 1990-1999 and 226,000 hospitalizations during 1979-2001 have been associated with influenza epidemics (1,2). Influenza viruses can cause disease among persons in any age group (3-5), but rates of infection are highest among children. Rates of serious illness and death are highest among persons aged >65 years, children aged <2 years, and persons of any age who have medical conditions that place them at increased risk for complications from influenza (3,6-8). Influenza vaccination is the most effective method for preventing influenza virus infection and its potentially severe complications. Influenza immunization efforts are focused primarily on providing vaccination to persons at risk for influenza complications and to contacts of these persons (Box). Influenza vaccine may be administered to any person aged >6 months to reduce the likelihood of becoming ill with influenza or of transmitting influenza to others; if vaccine supply is limited, priority for vaccination is typically assigned to persons in specific groups and of specific ages who are, or are contacts of, persons at higher risk for influenza complications. Trivalent inactivated influenza vaccine (TIV) may be used for any person aged >6 months, including those with high-risk conditions. Live, attenuated influenza vaccine (LAIV) currently is approved only for use among healthy, nonpregnant persons aged 5-49 years. Because influenza viruses undergo frequent antigenic change (i.e., antigenic drift), persons recommended for vaccination must receive an annual vaccination against the influenza viruses currently in circulation. Although vaccination coverage has increased in recent years for many groups recommended for routine vaccination, coverage remains unacceptably low, and strategies to improve vaccination coverage, including use of reminder/recall systems and standing orders programs, should be implemented or expanded. Antiviral medications are an adjunct to vaccination and are effective when administered as treatment and when used for chemoprophylaxis after an exposure to influenza virus. Oseltamivir and zanamivir are the only antiviral medications currently recommended for use in the United States. Resistance to oseltamivir or zanamivir remains rare. Amantadine or rimantidine should not be used for the treatment or prevention of influenza in the United States until evidence of susceptibility to these antiviral medications has been reestablished among circulating influenza A viruses. |