TCFL5 and influenza: In addition, since our previous studies demonstrated that addition of the AS03 adjuvant to the cHA-based influenza split IIV vaccine substantially improved antibody titers against the HA stalk (both IgG and IgA in serum) and against the N1 neuraminidase (NA) in mouse (32) and ferret models (19), AS03 was included in all IIV vaccines in this preclinical study.