Viruses can and do mutate. They contain DNA or RNA, and transcription errors can and do occur. Whether or not these result in a viable and virulent virus is a statistical thing.
What viruses have in their favor is that upon infection, the infected entity (cell or bacterium) essentially shuts down to produce viruses, and dies trying. Upon cell death, an enormous number of viruses are subsequently released.
So its "a numbers" game. Out of trillions of virus particles millions have defects, and out of millions one or two are viable and virulent. (Perhaps I have my numbers slightly off, but you get the point).
See:
http://www.kcom.edu/faculty/chamberlain/Website/Lects/PROPERT.HTM
Particularly see:
DNA virus replication -with the exception of the poxviruses, all DNA viruses replicate in the nucleus. In some cases one of the DNA strands is transcribed (in others both strands of a small part of the DNA may be transcribed) (step 4) into specific mRNA, which in turn is translated (step 5) to synthesize virus-specific proteins such as tumor antigen and enzymes necessary for biosynthesis of virus DNA. This period encompasses the early virus functions. Host cell DNA synthesis is temporarily elevated and is then suppressed as the cell shifts over to the manufacture of viral DNA (step 6). As the viral DNA continues to be transcribed, late virus functions become apparent. Messenger RNA transcribed during the later phase of infection (step 6) migrates to the cytoplasm and is translated (step 7). Proteins for virus capsids are synthesized and are transported to the nucleus to be incorporated into the complete virion (step 8).
In other words, the protein coat is most definitely genetically determined and specific to the virus.
Also google "virus protein coat" for a bunch of other interesting links.
The "goal" here is to have a large exposure to bird flu by people who are
also being exposed to human flu so one can play the probability game. There is a chance that the specific combination of bird flu and human flu when present in the same cell, will mutate into a virus with the virulence of the bird flu (so it contains deadly bird flu genetics) with the protein coat of human viruses (so it will penetrate human cell membranes) and become infectious.
Voila, you have pandemic.
If that doesn't work well because either the genetics are too dissimilar or the combination of exposures is not happening at a sufficient rate, then alternate plan 'B' "OOPS! I dropped the experimental vial on the floor, but we will let the cleaning people mop it up..." or plan 'C' "I mailed the deadly virus to so-and-so but it seems like it got lost by UPS".
Either way, with all of the incredible media hype, when it happens it becomes just another "see I told you so" and makes people more willing to believe "we're from the government and we're here to help you".
