Needle-free vaccine injection

Millions of people die each year from infectious disease, with a main stumbling block being our limited ability to deliver vaccines to optimal sites in the body. Specifically, effective methods to deliver vaccines into outer skin and mucosal layers--sites with immunological, physical and practical advantages that cannot be targeted via traditional delivery methods--are lacking. This chapter investigates the challenge for physical delivery approaches that are primarily needle-free. We examine the skin's structural and immunogenic properties in the context of the physical cell targeting requirements of the viable epidermis, and we review selected current physical cell targeting technologies engineered to meet these needs: needle and syringe, diffusion patches, liquid jet injectors, and microneedle arrays/patches. We then focus on biolistic particle delivery: we first analyze engineering these systems to meet demanding clinical needs, we then examine the interaction of biolistic devices with the skin, focusing on the mechanical interactions of ballistic impact and cell death, and finally we discuss the current clinical outcomes of one key application of engineered delivery devices--DNA vaccines.