Often, influenza outbreaks kill young people, or the elderly, or those patients that are already weakened. This was not the case for the 1918 pandemic, which killed mainly healthy young adults. Modern research, using virus taken from the bodies of frozen victims, has concluded that the virus kills through a cytokine storm (overreaction of the body's immune system). The strong immune reactions of young adults ravaged the body. But, the weaker immune systems of children and middle-aged adults caused fewer deaths among those groups.