DNA-based immunization mimics live-attenuated virus vaccination by stimulation of both the humoral and cellular arms of the immune system; thus, potentially providing the advantages of a live virus vaccination but without the potential risks. It is essential that novel vaccine strategies (including DNA-based immunizations) continue to be developed and enter Phase I human testing because to date, no candidate vaccine from any of the approximately 30 AVEG Phase I or II trials has progressed to a Phase III efficacy trial. Use of a Biojector jet gun for vaccine delivery may also have potential psychological, comfort, safety and immunologic advantages over the traditional needle and syringe method of delivery.