HA is the major glycoprotein of the influenza virus; it binds sialic acid on the surface of the cells through its globular head (HA1 domain) and makes possible the fusion of the viral envelope with the endosomal membranes through its stalk region (mainly formed by the HA2 domain) [17] . The sixteen known subtypes of HA, sharing between 40% and 60% amino acid sequence identity, have been clustered in two distinct phylogenetic groups: group 1 (H1, H2, H5, H6, H8, H9, H11, H12, H13, and H16) and group 2 (H3, H4, H7, H10, H14, and H15) [12, 14] . The subtypes, H1, H2, H5 and H9 in group 1, and H3 and H7 in group 2 have been isolated in humans and in particular H1, H2 and H3 subtypes have been responsible of the reported influenza pandemic outbreaks. In this study, we describe a human mAb, named PN-SIA28, that is capable of neutralizing all tested group 1 isolates, as well as isolates belonging to H3N2, the only group 2 subtype capable, so far, of causing a pandemic.