The current H1N1 virus is unique although it has some similarities to more and less virulent strains that have affected the human population in the past.
The Centers For Disease Control and Prevention says the virus is a very unusual four-way combination of human genes and genes from swine viruses found in North American, Asia and Europe.
Dr. Harvey Richey of the Texas Tech Medical School says, "The influenza virus mutates fairly rapidly, that is it changes it's character fairly easily. As it changes, its character it may become more vicious, if you will, or less so. And we just have to wait and see where we are with this virus."