Recent biochemistry studies have shown that NA in licensed influenza vaccines can now be quantified by stable isotope dimethyl labeling in conjunction with mass spectrometry.7 Published studies have also shown that inactivated vaccines can contain other viral components such as matrix protein (M1) and nucleoprotein (NP) and can elicit both CD4 T cell and antibody responses to inactivated influenza vaccination.8–12 These studies have suggested the potential of these induced specificities to provide broadly protective immunity to influenza. Here, XK is linked to influenza.