Department of Medical Education, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran.
Appropriate vaccine administration is essential to achieve optimal safety and efficacy in vaccination. It is necessary to administer the vaccine to the correct site and use the appropriate injection technique. Injecting too far to the side of the arm or too low on the arm risks tearing into the axillary or the radial nerve. This can cause burning or shooting pain during the procedure and lead to nerve damage (neuropathy/paralysis). The COVID-19 vaccine should be injected into the deltoid muscle in the upper arm in its central and thickest portion. If the muscle mass in the area of the deltoid is insufficient or for a particular reason the deltoid muscle is unsuitable, the alternative can be the injection into the vastus lateralis muscle in the anterolateral aspect of the thigh. Injection technique, choice of needle length and gauge (diameter), and injection site are important considerations as they can affect the immunogenicity of the vaccine and the risk of local reactions at the injection site.