To determine whether polyclonal Ig preparations from healthy plasma donors could be applied to prevent currently circulating and antigenically distant influenza infections in vivo, we first tested all four Ig preparations against Cal7 and PR8 viruses in vitro for the presence of anti-hemagglutinin antibodies in a hemagglutinin inhibition (HI) assay, for neuraminidase (NA)-inhibiting antibodies in a fluorescence-based assay and for virus-neutralising antibodies in a plaque reduction assay. Here, XK is linked to influenza.