Regarding how long a tetanus shot lasts, it depends on which type has been administered. Generally, there are two types of tetanus injections: tetanus immunoglobulin and tetanus antitoxin. Typically, doctors perform a skin test before administering the tetanus antitoxin; if the patient has a positive skin test and cannot tolerate desensitization treatment, tetanus immunoglobulin can be administered instead. These two medications have different metabolic times and their preventive effects vary. The metabolic time for tetanus antitoxin is generally one week, whereas for tetanus immunoglobulin, it can last about 28 days. Therefore, how long a tetanus shot lasts depends on the specific circumstances of the patient’s injection.