If your arm is swollen and painful after vaccination, you can use hot compresses or local topical medications to treat it. 1. Can be used to use hot compresses for treatment, such as warm gauze, towels, hot compresses vaccination site. You can also use fresh potatoes cut into slices and apply them to the red and swollen areas, usually the hardness can gradually subside, but be careful not to scratch with your hands to avoid infection. 2. If there is an allergic reaction to the vaccine or if the arm on the side of the vaccination comes into contact with some kind of substance that causes allergy, there will also be arm swelling, hardness and pain, and it is recommended that the patient go to the hospital in a timely manner, and follow the doctor’s instructions to use anti-allergy medication, such as applying glycerite lotion, oral loratadine, chlorpheniramine maleate and other therapies. The use of medication should be under the guidance of a doctor.