Additionally, several other known antigenic regions, partially derived from surviving patients of previous flu outbreaks (e.g. H5N1), are reported in the literature [44] [45] [46] and their location is indicated in the alignment ( Figure 5 ). Another extensive source of epitopes and antigens includ-ing neuraminidase of influenza A viruses is the immune epitope database (IEDB) [47] and the complete mapping of epitopes for the new H1N1 NA sequence is available at http://mendel.bii.a-star.edu.sg/SEQUENCES/H1N1/. While several of the new mutations are found in antigenic regions, it is also apparent that they often occur on positions that are hardly conserved among different NA subtypes. Consequently, these regions are evolutionarily more flexible and may mutate fast. This increases the risk of evading antibody responses of human hosts acquired during previous flu infection or from vaccination.