Most drugs injected into the muscles are meant for sustained absorption through the muscle vasculature and consequent drug distribution to body tissues helps them reaching their target sites to exhibit a therapeutic effect. However, unlike many drugs that are injected into the muscles, vaccines are not designed for absorption and distribution into the systemic circulation. Once injected into the muscles, the Covid vaccines spur an immune response against vaccine transfected cells. The antigen, lymphocytes and antigen-presenting cells drain through lymphatics into lymph nodes leading to humoral and cellular immune responses following vaccination. The Covid vaccines absorption into systemic circulation may lead to vaccine distribution and transfection in distance tissues beyond the injection site, which can cause serious adverse effects including auto-immune reactions against distance tissues. Some of the examples of rare but severe adverse events that are reported recently following Covid immunisation include: Guillain-Barré syndrome (GBS), myocarditis/pericarditis, vaccine-induced immune thrombotic thrombocytopenia (VITT) such as cerebral venous sinus thrombosis (CVST) or the splanchnic vein thrombosis (SVT). These reactions may be associated with inadvertent vaccine distribution and transfection to tissues away from the injection site. It was, therefore, cautioned that intramuscular injection of Covid vaccine should be done with aspiration technique to avoid inadvertent vaccine administration into deltoid muscle vasculature to prevent vaccine distribution to distance tissues. This may help improving vaccine safety by reducing the risk of developing rare severe adverse reactions to Covid vaccines.