Complete CoDing Sequences (CDS) of HA (1701 nt) and NA (1410 nt) genes corresponding to 2009 H1N1pdm, isolated from humans, were downloaded from the Influenza Virus Resource (http://www.ncbi.nlm.nih.gov/genomes/FLU /SwineFlu.html) from the National Center for Biotechnology Information, by the year of sequence repository. The first dataset consisted of 3765 HA and 2996 NA sequences, respectively, which were reported in the period 2009-2010. After discarding exact duplicates in sequence using a Perl script, we obtained 2038 HA and 1273 NA sequences, respectively; these sequences were different in at least one nucleotide among all representatives. Reassortant strains were discarded, as well as incomplete CDS sequences.