Influenza, commonly referred to as "the flu", is an infectious disease caused by an RNA virus that belongs to the Orthomyxoviridae family (the influenza viruses). This family of viruses affects both birds and mammals. Common symptoms of the disease are chills, fever, sore throat, muscle pains, severe headache, coughing, weakness/fatigue and overall general discomfort. Although Influenza is often confused with other respiratory virus illnesses, such as the common cold, influenza is more severe than the common cold and is caused by a different type of virus.
Influenza is a serious public health and economic problem which spreads worldwide in seasonal epidemics, resulting in the deaths of up to 500,000 people every year, and deaths in the millions in some pandemic years. Between 1979 and 2001, 41,400 people died from influenza each year in the United States on average. With the change in reporting the 30-year death estimates by the U.S. Centers for Disease Control and Prevention (CDC) in 2010, the current estimates for influenza are now reported to be from 3,300 deaths to 49,000 per year. The World Health Organization (WHO) estimates that the economic impact of influenza in the U.S. alone ranges from 71 to 167 billion dollars annually.