Topical immunization strategies.

Research has yielded an abundance of vaccine candidates against mucosal infections, but only few mucosal vaccines have been registered for human use. Extensive research is being carried out to identify new and safe adjuvants for mucosal immunization, novel delivery systems, including live vectors and reporter molecules for tissue- and cell-specific targeting of vaccine antigens. If these candidates are to reach those in need, several lessons from clinical and field research carried out under resource-poor settings must be considered. These lessons include the need to develop new vaccines that can be administered topically onto the skin or to the mucosa, without needles or expensive delivery devices. Such topical vaccines must be able to protect all age groups at risk, be safe and effective in immunocompromised people, and be able to contain epidemics following complex emergencies. The anatomical compartmentalization of immune responses imposes constraints on the selection of topical route(s) of vaccine administration and on strategies for measuring these responses, especially in young infants. Thus, the selection of any particular route of immunization is critical when designing and formulating vaccines against organ-specific infections.