XK and influenza: Although influenza NAs are divided into three phylogenic groups–influenza A group 1 (N1, N4, N5, and N8 subtypes), influenza A group 2 (N2, N3, N6 N7, and N9 subtypes), and influenza B (Ancestral-, Yamagata-, and Victoria-lineages) (Fig. S1)–most of the amino acids in the active site of NA are highly conserved across all three groups21.