The Spanish Flu

The 1918 Spanish Flu that killed up to 50 million people worldwide caused a severe immune response which may help to explain why it was so deadly, American scientists said on Wednesday.

The pandemic was one of the worst in recorded history and killed more people than World War I. But researchers did not understand what made it so lethal.

By infecting mice with a reconstructed version of the 1918 virus and monitoring their response, a team of scientists believe they have found some clues to solve the puzzle as well as a possible new way to fight pandemic flu.

"What we think is happening is that the host's inflammatory response is being highly activated by the virus, and that response is making the virus much more damaging to the host," said Dr John Kash, of the University of Washington in Seattle, who headed the research team.

"It is an overblown inflammatory response," he added in an interview, adding that it could have caused a similar immune response in humans.

Read more about the Spanish Flu here.