Route of Administration
The immunological response to a vaccine is dependent on the route of administration. Most current vaccines are administered intramuscularly or subcu-taneously, with some exceptions such as live polio vaccine and live typhoid vaccine, which are adminis-tered orally. Parenteral immunization usually induces systemic immunity. However, mucosal (e.g., oral, intranasal, or intravaginal) immunization may be preferred, because mucosal surfaces are the common entrance of many pathogens. The induction of a mucosal secretory IgA response may prevent the attachment and entry of pathogens into the host. For example, antibodies against cholera need to be in the gut lumen to inhibit adherence to and colonization of the intestinal wall. Moreover, mucosal immunization is attractive because it may induce both mucosal and systemic immunity. For example, orally administered Salmonella typhi not only invades the mucosal lining of the gut, but also infects cells of the phagocytic system throughout the body, thereby stimulating the production of both secretory and systemic antibodies, as well as CMI. Additional advantages of mucosal immunization are the ease of administration and the avoidance of systemic side effects (Shalaby, 1995; Bouvet et al., 2002; Walker, 2005). Up to now, however, successful local immunization has only been achieved with a limited number of oral vaccines. The formula-tion of the antigens is probably crucial for the success of mucosal immunization.
Apart from mucosal routes research groups are working on needle free jet injection of powders and fluids and dermal delivery with micro needles (Kersten and Hirschberg, 2004). A prerequisite of these approaches is that they must be painless. In that case several immunizations can be given with mono-valent vaccines, replacing one multivalent vaccine. Up to now these products have not yet been registered.