Developments in specialty vaccines will offer many new options in the future, while identification of new strains of viruses will provide endless research and profit potential for universities and pharmaceutical companies alike...» (doggedblog.com)
Influenza pandemics occur when a totally new strain of the virus emerges, against which nobody's immune system is fully prepared; that's why both the healthy and the weak are vulnerable. (sciencemag.org)
Plus, mutations cause a thus - far eternal number of new strains of the virus (treehugger.com)