Flu kills an estimated 23,000 people every year in the United States, almost all during the three or four month "flu season" from December to March. Ninety to 95% of those who die from flu are over age 65. The risk for death rises substantially for every decade in age beyond 65. The mortality rate from the H1N1 Swine flu that caused our recent pandemic was quite different. Very few people over age 65 were infected by Swine flu, and fewer still died from it. Almost 90% of the deaths from Swine flu were in people under age 65, and a large number were under age 25, a highly unusual development. However, as of December 2010 the pandemic strain of flu represented only 10% of circulating influenza viruses. Seasonal flu types and subtypes such as flu B and A(H3N2) have taken their usual place as the most commonly isolated flu viruses this season.
Hospitalization for flu in adults mirrors the mortality curve in that the elderly are considerably more likely to be hospitalized, with marked increases in hospitalization rates with each additional decade beyond age 65. Patients over age 85 are hospitalized at a rate of over 1 in 100.