Having learned how to jump from birds to humans, the H5N1 avian flu virus may be poised to launch the next great pandemic. The deadly virus has sickened people in eight Asian countries who tend flocks of chickens and ducks. The mortality rate among diagnosed people may be as high as 72%.

As it evolves, the virus may soon become transmissible from human to human, letting it spread rapidly around the world. The great flu pandemic of 1918, which was triggered by another virus originating in birds, killed 20 to 40 million people worldwide.

An avian flu vaccine developed by Sanofi Pasteur is ready for preliminary clinical trials; Sanofi is also involved in a European vaccine project called Flupan. The Centers for Disease Control and Prevention is stockpiling antiviral drugs and working with the World Health Organization to increase its monitoring of flu outbreaks in Asia. Anthony Fauci, MD, director of the National Institute for Allergy and Infectious Diseases, said the Sanofi vaccine could be made available for emergency use if needed.