The duration of a tetanus shot can be considered from two different immunization processes.

In the case of passive immunity, it typically lasts for a shorter duration. If tetanus antitoxin is administered, it generally lasts between two to four days, while tetanus immunoglobulin can last up to three weeks. After this period, the level of antibodies gradually decreases, and the body may no longer be protected. Therefore, a single use of tetanus antitoxin or immunoglobulin does not provide lasting immunity.

The second method is what we commonly refer to as getting a tetanus vaccine, which is a process of active immunity. Usually, for active immunity, the tetanus bacterium is processed and made into a weakened vaccine for injection. Antibodies can be produced after about ten days, and within two to three months, the level of antibodies in the body gradually increases and remains at a high titer, providing immunity for up to about ten years.