Side effects from tetanus shots are rare, but they can include localized side effects at the site of the injection in the arm, including redness, soreness and swelling, according to WebMD. The shot can also cause a fever, headaches, body aches and fatigue. In some cases, the shot can cause a severe allergic reaction that requires immediate medical attention.
Anaphylaxis is an allergic reaction, and tetanus shots are an uncommon but potential trigger, according to WebMD. Anaphylaxis sometimes begins as severe itching of the face, including the eyes, and it can escalate quickly to other symptoms such as problems swallowing and breathing, and it can cause hives or angioedema, which is hives under the skin. Other potential symptoms include nausea, vomiting, abdominal pain and cramps. Suffers might also have low blood pressure, a fast heartbeat and a feeling of weakness.
If left untreated, anaphylaxis can lead to shock and unconsciousness, and it's potentially deadly, according to WebMD. Treatment typically involves giving the patient adrenaline through an epinephrine shot to reverse the most dangerous symptoms. Sufferers might also need CPR or other measures. People who think they or someone they're around is suffering from anaphylaxis should call 911 immediately and report information about the tetanus shot or other potential triggers.