Lvov is thinking about just a single change of an amino acid, maybe the G228S that Niman is worried about. G228 is a glycine to serine change in position 228 of the hemagglutinin protein chain HA1. The S227N described below is a serine to asparagine change in position 227, and it increases the ability of the virus to attach itself to mammalian respiratory cells (like in you and me)
http://www.recombinomics.com/PR/021706.html
"The donor sequences are again on the H, but in H1N1 European swine sequences. The new genetic change, G228S, has also been previously shown to increase the affinity for human receptors. Like H9N2 in the Middle East, H1N1 is endemic in swine populations in Europe. Infection by H5N1 in H1N1 infected swine will allow the viruses to exchange genetic information via recombination and allow H5N1 to acquire S228N. The region of identity between H5N1 and H1N1 is downstream from the S227N position, so H5N1, with and without the S227N change, can acquire this new sequence. This sequence acquisition by the H5N1 virus will also lead to more efficient transmission to humans."
Not nice!