It was suggested that the particularly distinctive receptor-binding specificity of H16 viruses may be related to their HAs containing A138S (found in human 1977-derived H1N1 viruses, reducing binding to α2,3Neu5Ac receptors) and E190T (the amino acid (aa) at position 190 determining binding specificity of H1N1 viruses to the sialyl linkage type) [23].