From MSNBC:
The 1918 Spanish flu killed at least 20 million people around the globe. Fears of a similar pandemic have health officials concerned the death toll could be much higher in a modern outbreak, which researchers say is very likely if the current deadly bird flu morphs into a strain that can be transmitted by humans. Travel between countries has become vastly more frequent and quicker, which would hasten the spread of a highly contagious and lethal virus. In the last of a three-part series, LiveScience examines how a virus jumps from birds to humans and reaches pandemic proportions.
More here.