World Health Organization
To date, extensive testing by laboratories in the WHO influenza surveillance network has detected no signs that the H1N1 pandemic virus has mutated to a more virulent form. Currently licensed pandemic vaccines closely match circulating viruses and are expected to confer good protection.
Vigilance for changes in the H1N1 virus includes monitoring to detect possible influenza infections in susceptible animals, both mammals and birds, as well as humans. While most influenza A viruses circulating in mammals preferentially infect a single species, cross-species transmission is known to occur.
Read more here.