By Oliver Conway
The flu outbreak of 1918 killed an estimated 50 million people
Survivors of the devastating 1918 influenza pandemic are still protected from the virus, according to researchers in the US.
American scientists found that people who lived through the outbreak can still produce antibodies that kill the deadly strain of the H1N1 flu.
The study, published in the journal Nature, could help develop emergency treatments for future outbreaks.
The Spanish flu outbreak of 1918 killed an estimated 50 million people.
Some experts say it was the most devastating epidemic in history, affecting even healthy adults.
Scientists do not fully understand why it was so lethal - but they fear a new pandemic, once again triggered by bird flu, could be just as deadly.
But now researchers have come up with a new way of tackling such an outbreak.
They studied 32 people who lived through the 1918 flu, and found all still had antibodies in their blood to destroy the virus.
Some of the volunteers - aged from 91 to 101 - even had the cells which produce the antibodies.
The researchers used the antibodies to cure infected mice - showing, they said, that 90 years on, the survivors of the epidemic were still protected.
The antibodies were particularly powerful - so that only a small amount was needed to kill off the virus.
Dr James Crowe, of Vanderbilt University, who helped lead the study, said similar antibodies could be developed to destroy new strains of bird flu.