DNA vaccination is an attractive strategy to provide relatively quick and straightforward production of vaccines against an influenza pandemic when the demand for such vaccines suddenly increases. However, a key issue surrounding the use of DNA vaccines is their low immunogenicity in humans. In recent years, the success of the prime-boost strategy has greatly enhanced the utility of DNA vaccination for future human applications [10, 30] . At the same time, optimization of the design of antigen inserts based on the uniqueness of each antigen (a process of ''antigen engineering'') [31, 32] can also play a key role.