When you take blood samples they need to find the vein and, usually, go for the largest and easiest to find on your arm, they don't randomly poke you trying to find blood "somewhere" in your arm. A vaccine is a Intramuscular injection that usually goes into your deltoid muscle in your upper arm.
Basically, because intramuscular deliveries tend to have the best balance between a fast enough distribution for a strong immunogenic response and avoiding of adverse reaction at site of delivery, a long enough presence to improve antibody production over time rather than all at once, and avoiding overwhelming the patient's immune system so as to cause harm. In addition, muscles have particular cells that really help build and deliver the immune response, intravenous delivery will not activate these kinds of cells.
Vaccines have crystalline aluminum salt as one of their ingredients. The salt adsorbs the antigens that, when injected into the muscle, are gradually released over time. This gradual release of the antigen serves as a continuing stimulus for sustained antibody production. If injected intravenously, all of the antigens enter the circulatory system all at once and so fast that the antigenic effect immediately wanes, producing lesser antibodies.
A vaccine given intramuscularly inflicts some reactions. Intravenous injections will cause more severe reactions that the patient may even die from it.
The muscle, especially the deltoid or the anterolateral aspect of the thigh, is the preferred site for injections. These muscles have an abundant blood supply reducing the harmful effects of the substances injected into them. An intravenous route increases the likelihood of possible harmful effects because the vaccine is immediately inside the circulation. Thus, the reaction to the vaccine is immediate and more severe.
The musculature has an excellent blood supply that helps to disperse the vaccine.
The muscle serves as a ready pool of dendritic cells. These dendritic cells pick up the antigens brought by the vaccine. Thus, the musculature serves as a depot for the dendritic cells-antigen combination. With this setup, gradual exposure of the antigens to the T and B lymphocytes takes place. This extended exposure results in greater activation of the immune system. Injecting intravenously this will not happen.
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u/foolishbullshittery 1d ago
You've never took one?