Tetanus is caused by a bacteria that enter the body through wounds in the skin. The bacteria produce a toxin that causes septic muscle contraction . Death often results from failure of the respiratory system . A patient comes to the emergency room after stepping on a nail. If the patient have been vaccinated against tetanus , he is given a booster shot, which consist of the toxin altered so that it is harmless. If he has never been vaccinated against tetanus he is given an antiserum shot against tetanus . Explain the rationale for this treatment strategy.