A method for producing an α-Gal-expressing virus having enhanced immune response to viruses, without requiring the use of any enzyme an influenza virus vaccine having a high effect (antigenicity), which is produced using an α-Gal-expressing virus produced by the method and others. Specifically disclosed are: a method for producing an α-galactose epitope (Galα1-3Galβ1-4GlcNAc-R: α-Gal hereinafter)-expressing virus, which comprises the steps of: (1) introducing an α1,3- galactosyltransferase gene in an expressible condition into a cell line that does not express α-Gal to obtain a cell line capable of expressing α-Gal(2) inoculating a virus into the cell line capable of expressing α-Gal to obtain a cell line infected with a virus and(3) culturing the cell line infected with the virus to obtain a virus expressing α-Gal from the culture medium..
