Provided herein are methods for generating a non-naturally occurring, broadly reactive, pan-epitopic antigen derived from H3 influenza virus that is capable of eliciting a broadly reactive immune response, such as a broadly reactive neutralizing antibody response, against H3 virus following administration to a subject. Also provided is a non-naturally occurring immunogen generated using the methods, and vaccines and compositions comprising the immunogen. Methods of generating an immune response in a subject by administering the immunogen, vaccine, or composition are provided. In particular, the immunogen comprises the hemagglutinin (HA) protein of H3 influenza virus strains.