Scientists identify key factor in switch from birds to humans British scientists have solved a secret of an avian flu virus which killed up to 40 million people worldwide 86 years ago. They now know more about how a disease of birds switched to humans to trigger the most lethal outbreak in history. A team from the National Institute for Medical Research at Mill Hill, north London, used pathological samples taken from victims of the Spanish influenza pandemic of 1918 to recreate the structure of a haemagglutinin protein vital in the leap between species. "This tells us more about the...