2 - PB2, PB1 and PA polymerase genes of 6 A / H5N1 influenza virus strains, ie. A / Duck / VietNam / QT801/2011 (H5N1) and A / Duck / VietNam / QT802/2011 (H5N1) (clade 2.3.2.1), A / Duck / VietNam / NA72/2007 (H5N1) and A / Duck / VietNam / NA114/202007 (H5N1) (clade 2.3.4.3), A / Chicken / VietNam / DT382/2008 (H5N1) and A / Duck / VietNam / TG926/2009 (H5N1) (clade 1.1), have a high homology rate (%) of nucleotide (96% - 99%) and and amino acid (98% - 99%), in oder respectively, in comparision with the corresponding genes of clades 2.3.2.1, 2.3.4.3 and 1.1 of A / H5N1 viruses isolated from 2007 to present.