Vaccine Delivery Systems: Roles, Challenges and Recent Advances

The overwhelming majority of vaccine antigens are biological macromolecules, such as proteins and polysaccharides, typically with a molecular weight greater than 10,000. As such, they need to be delivered to the body in the correct conformation in order to elicit the desired immune response and to effectively target the immune cells. Currently, most vaccines are administered parenterally via the intradermal, subcutaneous or intramuscular route, the choice largely dependent on whether the antigen is in the adsorbed or nonadsorbed state. However, these routes have major drawbacks, including pain associated with the use of needles, the potential for needle contamination, practicalities of needle disposal and the need for a primary healthcare worker. There is now a particular focus on the development of mucosal vaccines, designed for direct application to mucosal surfaces such as those present in the mouth, nose, vagina and rectum.