Transdermal delivery of vaccines - Recent progress and critical issues.

In 2010, the number of deaths from infectious diseases globally was approximately 15 million. It has been reported that two-thirds of deaths from infections are caused by around 20 species, mainly bacteria and viruses. Transnational migration caused by war and the development of transportation facilities have led to the global spread of infectious diseases. Subcutaneous vaccination, though widespread, has a number of problems: the need for trained healthcare personnel, pain, needle-related injuries as well as storage difficulties. Two layers of the human skin- epidermis and dermis- are populated by dendritic cells (DCs), which are potent antigen-presenting cells (APCs). Transcutaneous immunization has therefore become an attractive and alternative route for vaccination. In this review, the various techniques for enhancing vaccine delivery are discussed. These techniques include iontophoresis, elastic liposomes as well as microneedles. Progress made so far with these techniques and the critical issues facing scientists will be highlighted.