Arm soreness after vaccination is a common adverse reaction after vaccination, and may be accompanied by hard nodules and redness at the injection site, which generally will gradually subside on its own, so there is no need to worry too much. 1. Needle stimulation: When vaccinating, if the vaccinator is not relaxed enough, the muscles are in a tight state when injecting, or the needle stimulates the peripheral nerves on the arm, it may lead to arm soreness, which generally will subside on its own after 1-3 days. 2. Stimulation of the surrounding tissues by the vaccine: In addition to the antigenic protein, the vaccine also contains some adjuvants, and the whole inactivated virus vaccine also contains inactivated nucleic acid, glycoprotein, phospholipid and other components, which may stimulate the nerves or muscles and cause arm pain. 3. The vaccine is not completely absorbed: mental tension during injection or heavy physical labor after vaccination will make the muscles tense, thus reducing the efficiency of vaccine absorption by the body, which may lead to local hard knots, redness and swelling or arm pain. Therefore, it is important to avoid rubbing the needle holes after vaccination, keep the muscles relaxed, and avoid heavy physical work. After the vaccine is absorbed, the local discomfort will be reduced and the arm pain will be relieved. After vaccination, you should also pay attention to a light diet, do not eat spicy, oily and other stimulating foods, pay attention to rest, drink more water, and use hot compresses to relieve pain if you have significant arm pain. If you have severe pain, you should go to the hospital in time to find out the cause, and do not take medicine at your own discretion.