The pandemic flu outbreak that swept the world in 1918 to 1919 was so deadly because of the severe immune response it caused in its victims, new research shows.
Scientists report in the Oct. 5 online edition of Nature that certain genes related to immune response and infection fighting were activated in victims, leading to what researcher John Kash called an "overblown inflammatory response."
"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 Kash, research assistant professor of microbiology at the University of Washington and lead author of the study. "The host's immune system may be overreacting and killing off too many cells, and that may be a key contributor to what makes this virus more pathogenic."
The 1918 to 1919 pandemic flu outbreak, which involved an H1N1 strain of avian influenza, is estimated to have killed 50 million people globally. Unlike the seasonal flu, which typically hits children and the elderly, the pandemic flu outbreak took a heavy toll on young adults with strong immune systems, leading researchers to wonder why it caused so many deaths in that population group.