It is very common to have swollen arms from vaccination. The main reason is that the solutes and solvents inside the vaccination needle cause obvious local inflammatory reaction, so there will be inflammatory cell infiltration, causing edema and sometimes accompanied by pain. If the symptoms are obvious, oral non-steroidal anti-inflammatory drugs, such as ibuprofen or diclofenac sodium, can be used to reduce local inflammation and relieve pain, and oral abortifacient or avelox can be taken at the same time to promote local venous reflux to reduce edema. If the symptoms are mild, you can also use hot compresses or physical therapy to promote the reduction of swelling in the arm, but if it is accompanied by local skin redness, more pain, more obvious swelling, and accompanied by body heat. In this case, you should go to the hospital as soon as possible, because there is a possibility of a combined local subcutaneous infection, which requires further examination and treatment.