Original sentence: The pandemic lasted from March 1918 to April 1920 , spreading even to the Arctic and remote Pacific islands.The weaker immune systems of young adults ravaged the body, whereas the stronger immune systems of children and middle-aged adults caused fewer deaths
Edited sentence: The pandemic lasted from March 1918 to June 1920 , spreading even to the Arctic and remote Pacific islands.The strong immune systems of young adults ravaged the body, whereas the weaker immune systems of children and middle-aged adults caused fewer deaths