The duration of the effectiveness of a tetanus shot depends on whether tetanus antitoxin or tetanus immunoglobulin is administered following a suspected tetanus infection. Both types are forms of artificial passive immunity, providing immediate specific immunity after injection, mainly for treatment or emergency prevention. The metabolism and immune duration of these two injections vary: generally, tetanus antitoxin lasts about seven days, while tetanus immunoglobulin can last up to three weeks. Therefore, the specific duration of the effectiveness of a tetanus shot must be determined based on the individual injection circumstances. For suspected tetanus infections, it is generally advised to administer the injection as soon as possible. It's not that the injection will be ineffective if administered after a certain time, but rather that effective prevention before the onset of the disease can still be beneficial.