XK and infection: For the 16 patients who had sequence-confirmed A/H1N1 infections, Cal09 NA- and bovine A/H5N1 NA-specific IgG were both substantially boosted by infection, albeit to different magnitudes (Fig. 3a and b), with a 151-fold increase in Cal09 N1 NA-binding antibodies and a 55-fold increase in bovine A/H5N1 NA-binding antibodies.