A Randomized Controlled Trial of Influenza Vaccine in the Elderly

Influenza viruses have arguably caused more morbidity and mortality than any infectious agent in recorded history. Seven pandemics of influenza have occurred during the past century alone, one of which—the infamous Spanish (swine) flu—was responsible for at least 20 million deaths worldwide. Of even greater concern has been the occurrence of annual epidemics of varying severity that have resulted in more than 599 000 excess deaths in the United States during the past 40 years.¹⁻³Although complacency regarding influenza is widely prevalent owing to the misperception that it is simply a mild respiratory or gastrointestinal infection,²one needs only to briefly examine accounts of recent outbreaks to appreciate the explosive potential for influenza viruses to cause life-threatening illness.⁴The unusual properties of the virus' genome, including a high frequency of point mutations (which cause the hemagglutinin [HA] and neuraminidase [NA] molecules to drift See also p 1661.