Influenza vaccination coverage among adults--National Health Interview Survey, United States, 2008-09 influenza season.

In the United States, annual influenza epidemics typically occur during the late fall through early spring. During these epidemics, rates of serious illness and death are highest among adults aged ≥65 years, children aged <2 years, and persons of any age who have medical conditions that increase their risk for complications from influenza. Adults aged 50-64 years who have underlying medical conditions have a substantially increased risk for hospitalization during the influenza season. Influenza illness among healthy adults aged 18-64 years typically is not as severe as the illness among adults aged ≥65 years, pregnant women, or persons with chronic medical conditions and less frequently results in hospitalization. However, influenza among healthy adults aged 18-49 years is an important cause of outpatient medical visits and worker absenteeism. An economic analysis estimated an annual average of approximately 5 million illnesses, 2.4 million outpatient visits, 32,000 hospitalizations, and 680 deaths from influenza among adults aged 18-49 years who did not have a medical condition that increased their risk for influenza complications. In this analysis, adults aged 18-49 years accounted for 10% of the total economic cost from influenza, or approximately $8.7 billion.