Genomic analysis of the 2009 infl uenza A (H1N1) virus in humans indicates that it is closely related to reassortant swine infl uenza A viruses isolated in North America, Europe and Asia [ Fig. 1 ] [9] [10] [11] . The segments coding for the polymerase complex, hemagglutinin, nuclear protein, and non-structural proteins show high similarity with the swine H1N2 infl uenza A viruses isolated in North America in the late 1990s. The segments coding for the neuraminidase and the matrix proteins of the new human H1N1 virus are, however, distantly related to swine viruses isolated in Europe in the early 1990s. In particular, the closest isolated relatives of the neuraminidase segment have 94.4% similarity at the nucleotide level with European swine infl uenza A virus strains from 1992 [11] .