Equine IgE responses to non-viral vaccine components

► IgE and/or IgG specific to bovine serum albumin (BSA) is induced in horses by viral vaccination. ► Adverse vaccine reactions are associated in some horses with high levels of IgE to BSA. ► Skin test and serum BSA IgE+ horses may not develop adverse clinical responses to vaccination. ► West Nile virus vaccine grown on Vero cells stimulates IgE to Vero cell antigens in some horses.