A swollen bag after tetanus shot may be related to allergy, swelling of soft tissues under the skin, and too fast speed during vaccination. 1. Allergy: some people may be allergic to tetanus vaccine, when the body begins to release inflammatory factors, it will cause congestion and edema of the tissues, which is manifested as a swollen bag after tetanus shot. 2. Subcutaneous soft tissue swelling: in the process of playing tetanus vaccine, the needle will pass through the skin, through the subcutaneous tissue into the muscle tissue, if the needle is thick or the local reaction is more sensitive, it will make the local muscle spasm, which will lead to the local tissue edema is more serious, which is manifested as a swollen bag of playing tetanus. 3. Playing the vaccine too fast: If the speed of playing the vaccine is too fast, the drug and liquid will accumulate locally in the muscle or tissue, and can not be absorbed by the body in time, which will lead to a swollen bag after playing the tetanus vaccine. Tetanus swollen bag after playing, should be timely consultation to understand the specific situation, under the guidance of the doctor to give targeted treatment.