Figure 1.

Immunization by cutaneous routes. A. Liquid-jet injection delivers vaccine to muscular, subcutaneous or dermal regions, depending on the parameters of the injection, B. Epidermal powder immunization delivers vaccine powders to the superficial layers of the skin, C. Topical application of vaccines delivers vaccines to the epidermis, where they are recognized and processed by Langerhans cells. Immunization by topical vaccine application is facilitated by several methods (a–h) (Reprinted with permission from Ref. [1]).