"In fact, some researchers thought the virus might just be unable to swap an amino acid at position 226 outside the lab. But then came the mysterious case of a severely sick teenager in Canada who has been hospitalized with H5N1 since early November. Virus sequences from that patient suggest some H5N1s had changed the amino acid at position 226 whereas others had not, says Jesse Bloom, an evolutionary biologist at the Fred Hutchinson Cancer Center. “It looks like during the infection of this individual, the virus could have been evolving towards at least some of the mutations that would adapt it to humans.” This was not the feared 226L mutation: The amino acid had changed to a histidine instead of leucine. Still, “It showed that those sites are mutable in these viruses,” says Tom Peacock, an influenza virologist at the Pirbright Institute. And the glutamine substitution, together with another mutation in the same virus at position 190, could have the same effect as the 226L. For Peacock and others, the finding upped concern about an imminent pandemic."

Source: Why hasn’t the bird flu pandemic started?