After receiving a tetanus shot, it generally lasts for about six months. However, if you are injured again after six months and the wound is heavily contaminated, such as with contaminated soil or rust, and the wound is large and deep, it is advised to undergo tetanus treatment again. The purpose of the tetanus shot is to prevent infection by Clostridium tetani, which is an anaerobic bacterium. It tends to proliferate in anaerobic environments and in conditions of heavy contamination by rust and soil. Therefore, if after tetanus treatment the injury is relatively minor, shallow, and comparatively clean, it is sufficient to clean and dress the wound and keep it dry. If the wound is heavily contaminated, large, and deep, it is recommended to administer the tetanus shot again.