Provided is a method for producing an influenza HA split vaccine that produces antibodies that bind to the HA stem region of influenza, which is less likely to undergo antigenic mutation. Acid treatment of the influenza HA split vaccine is performed. An influenza HA split vaccine that produces antibodies that bind to LAH of the HA stem region is obtained by performing acid treatment. This influenza HA split vaccine has excellent protective ability against influenza virus infections of different antigenicity.
