All influenza (flu) viruses have a relatively high mutation rate, however, scientists are particularly concerned about the highly pathogenic avian influenza (HPAI) subtype HPAI H5N1. The scope of their concern has broadened in recent months with the detection of HPAI H5N8 in North America, and outbreak of H5N2 in the United States. Avian influenza, in the presence of human or seasonal flu, has the potential to mutate and develop into a new subtype of virus. Globally, there would be little immunity to this new strain and it could have significant public health consequences. Influenza viruses mutate in two ways; antigenic drift and antigenic shift.
At this point, there is no evidence of genetic reassortment between avian H5N1, H5N8, or H5N2 viruses and human viruses; however, if these viruses continue to circulate widely among poultry, the potential for emergence of a reassorted pandemic strain remains a concern. A global influenza pandemic (worldwide spread) may occur if three conditions are met:
While the virus is not able to spread easily from person to person, it does cause severe disease. WHO places the current pandemic phase level at a 3, "no or very limited human to human transmission." However, the case fatality rate of HPAI H5N1 is 60 percent. In other words, 60 percent of those infected with HPAI H5N1 die. The potential for a mutation to increase the transmission rate is low; however, the implications it would have on public health would be great.