For effective vaccination, the vaccine must have access to the immune system. Ideally, vaccines would be delivered directly t ... o immune cells, such as into an immune organ. These immune organs include the lymph nodes, the spleen, or the skin itself. Immune cells do not normally reside in the muscle tissue. Even though the muscle is not the ideal location to elicit an immune response, the common practice is to administer vaccines intramuscularly. This convention is dominant in part because it is simply more practical to administer a vaccine precisely and accurately into the muscle. There is evidence that supports the comparative advantage of intradermal delivery over intramuscular delivery.* Intradermal vaccinations have demonstrated enhanced immune responses in some cases.** * 1. Teunissen, M. B., M. Haniffa, et al. (2012). "Insight into the immunobiology of human skin and functional specialization of skin dendritic cell subsets to innovate intradermal vaccination design." Curr Top Microbiol Immunol 351: 25-76. ** 2. Ogai, N., I. Nonaka, et al. (2018). "Enhanced immunity in intradermal vaccination by novel hollow microneedles." Skin Res Technol 24(4): 630-635. read more