Via the New York Times: Scientists Hope Vigilance Stymies Avian Flu Mutations.
Just exactly what is the bird flu virus doing?
The virus, H5N1, which was first isolated in humans in 1997, has not started a pandemic in a full decade of trying, so a few flu experts think it never will.
But the mainstream view is less optimistic. Viruses mutate constantly, many experts point out. And when one has already acquired the ability to jump species, occasionally spread from human to human and kill 60 percent of the people who catch it, it is far too early to dismiss it.
So even though the human death toll from H5N1 is still below 200, scientists around the world are racing to study the ways in which it might mutate to spread easily among humans.
The whole article is very much worth reading.