Smith, Andrewes, and Laidlaw isolated influenza a virus in ferrets in 1933, and Francis isolated influenza B virus in 1936. In 1936, Burnet discovered that influenza virus could be grown in embryonated hens’ eggs. This led to the study of the characteristics of the virus and the development of deactivated vaccines. The first live weakened influenza vaccine was licensed in 2003.Among the conclusions of this research is that the virus kills via a cytokine storm (overreaction of the body's immune system) which explains its unusually severe nature and the determined age profile of its victims. The strong immune systems of young adults withered the body, whereas the weaker immune systems of children and middle-aged adults caused fewer deaths.Despite
