Arm pain after vaccination is a common phenomenon after vaccination, which may be due to the adverse reaction of the vaccine itself, or it may be due to mental tension during injection and muscle tightness to produce painful reaction after injection, which will generally be relieved within a few days. The common causes of arm pain after vaccination are as follows: 1. Adverse reactions to vaccines: Vaccines can cause the body to produce specific immunity, thus preventing related diseases. Vaccine injections may cause arm pain due to nerve or muscle irritation, sometimes accompanied by adverse reactions such as redness, swelling and fever at the injection site. For example, after BCG vaccination, redness, swelling, pus and small ulcers may appear and eventually crust over and heal, sometimes accompanied by short-term mild febrile reactions; 2, mental tension during injection: mental tension during injection will subconsciously tense the muscles, and muscle tightness will make the vaccine components less efficiently absorbed by the body, which may lead to local hard nodules and redness or swelling, resulting in arm pain after vaccination. After vaccination, keep the needle holes clean, do not get wet or rub yourself, keep your muscles relaxed, and do not do heavy physical work. Pay attention to a light diet, avoid smoking and alcohol, and avoid spicy and oily food. For pain at the injection site, no special treatment is usually needed. If severe pain or high fever occurs, go to the hospital to find out the cause in time, and do not take medication to relieve it by yourself.