Most people experience mild side effects after receiving tetanus shots, including low fever, fatigue, swollen glands, nausea and muscle pain, according to WebMD. More serious side effects include nervous system problems, swelling of the arm where the injection was given and a high fever.
Some people experience an allergic reaction to the tetanus shot within several minutes of receiving it, explains WebMD. While this reaction only affects one in a million people, it can be life threatening and requires immediate medical attention. Signs of an allergic reaction include difficulty breathing, rapid heart beat, weakness, dizziness and behavior changes after receiving the shot.