Scientists who tested monkeys with the resurrected 1918 killer flu virus have a better idea of how the deadliest epidemic in history killed so many people: by overcharging the victims’ own immune systems. Those findings in a first-of-its-kind experiment also help explain why so many of the roughly 50 million who died in the flu pandemic were young and healthy. Scientists discovered the virus replicated quickly and unleashed an excessive immune system response in the macaques that destroyed the lungs in a matter of days. “Essentially people are drowned by themselves,” says University of Wisconsin researcher Yoshihiro Kawaoka, lead author of the study in today’s Nature. Scientists say the results open a window into what could happen if the current bird flu in Asia changes into a highly lethal strain that spreads easily among people.
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