Fusion antigen used as vaccine and method of making them. The method includes: (1) selecting a segment of a virus protein sequence that contains a least one epitope; (2) engineering a DNA fragment encoding the selected segment of the virus protein; (3) inserting the DNA fragment into a Pseudomonas Exotoxin A (PE) vector to obtain a chimeric gene plasmid, and expressing the chimeric gene plasmid in a host cell to obtain the chimeric vaccinal virus antigen. The PE vector contains a PE fragment, which has a binding domain and a translocating domain, and a carboxyl terminal moiety, which includes an endoplasmic reticulum retention sequence. The DNA fragment encoding the selected segment of the virus protein is inserted between the PE fragment and the carboxyl terminal moiety.