Millions Have Been Infected by H1N1

(February 15, 2010) - Tens of millions of Americans have been infected by the H1N1 virus, according to estimates released by the Centers for Disease Control and Prevention (CDC). The so-called swine flu (Read about "Influenza") has infected somewhere between 41 and 84 million people in the US by CDC estimates.

The United States experienced its first wave of 2009 H1N1 pandemic activity in the spring of 2009, followed by a second wave of 2009 H1N1 activity in the fall. Activity peaked during the second week in October and then declined.

The early rise in flu activity in October is in contrast to seasonal influenza. Influenza activity usually peaks in January, February or March. Because 2009 H1N1 activity peaked in late October, the greatest increase in the number of estimated 2009 H1N1 cases, hospitalizations and deaths occurred during the period of April through November.

CDC also estimates that between about 183,000 and 378,000 H1N1-related hospitalizations occurred during that time and between about 8,330 and 17,160 2009 H1N1-related deaths occurred.

CDC will often quote the midpoint on its estimates, which would be 57 million cases of H1N1, 257,000 hospitalizations and 11,690 deaths.

The data by age provided in the updated estimates continues to confirm that people younger than 65 years of age are more severely affected by this disease compared to people 65. With seasonal influenza, about 60 percent of seasonal flu-related hospitalizations and 90 percent of flu-related deaths occur in people 65 years and older. With 2009 H1N1, approximately 90 percent of estimated hospitalizations and 87 percent of estimated deaths from April through January 16, 2009 occurred in people younger than 65 years old.