system
Given the following post, respond as if you're commenting on Reddit:
human
How do tetanus vaccines (boosters) work?

A vaccine causes an active immune response, which leaves behind memory cells and results in immunity. I understand the concept of getting a "booster"  some time after to keep the immunity, but why do people need tetanus shots after getting a puncture wound. If the antigens are already in the body, is a response to the vaccine really going to help deal with a pathogen that has already breached the external defense? Or does the tetanus booster contain antibodies to help fight the infection?
gpt
For Tetanus specifically, it's not the bacterium that causes the damage. It's the toxins that the bacterium produces that do.  
*Clostridium tetani* produces an extremely powerful neurotoxin that causes Lockjaw. Basically, the toxin permanently paralyzes muscles, by blocking the shutdown signal. When/if this paralysis reaches the muscles responsible for breathing, the subject stops breathing.

The Tetanus vaccines specifically target the toxin, not the bacterium. Without the toxin, the bacterium is rather harmless and can be cleaned up by the natural response.

Boosters after a wound are given in the case of the patient being unsure if they got a booster in the last 10 years (or if they know they didn't). If the patient hasn't received the full 3 lifetime vaccination shots yet (3 is needed for maximum immunity), then active antibodies can be added to ensure immediate cleanup of toxins.

Giving a booster shortly after potential infection can kickstart the production of antibodies by the immune system, before the infection has had a chance to build up to lethal dosage, and help the immune system notice the infection quicker (basically, you kick someone to alert them to the killer across the street)