Seasonal influenza is a highly communicable, acute viral infection that predominantly attacks the respiratory tract and sometimes the lungs. It can cause mild to severe illness and can lead to death. Up to 5 to 15 percent of the worldwide population is infected each year and approximately 250,000 to 500,000 die. More than 90 percent of deaths associated with influenza in industrialized countries occur among those 65 years of age and over.