Laboratory-confirmed influenza-associated hospitalization rate for different age groups, during the 2009 (H1N1) pandemic influenza period and recent seasonal influenza periods, in the United States of America.*

Abbreviations: m: months, NA: non-available, y: years, wks: weeks.* Data are from US Centers for Disease Control and Prevention; Emerging Infections Program (EIP) (http://www.cdc.gov/flu/weekly/fluactivity.htm).∧ Rates for new EIP sites are not included.