Why does a vaccine make us immune to a pathogen?

• A. If the same pathogen enters again, white blood cells respond quickly to produce antibodies faster, preventing infection.
• B. Vaccines kill all pathogens in the body.
• C. Vaccines replace the immune system.
• D. Vaccines make pathogens weaker.

Answer: (B)

Vaccines prime the immune system to recognize a pathogen by exposing it to a safe form or part of the invader. This triggers the formation of memory cells—memory B cells that can rapidly produce antibodies and memory T cells that coordinate the response. When the real pathogen is encountered later, these memory cells respond quickly and strongly, generating antibodies and activating other defenses fast enough to prevent infection or greatly lessen its severity. The vaccine’s job isn’t to kill pathogens already in the body, and it doesn’t replace or weaken the immune system. It trains the body to respond more efficiently on future exposures, which is why immunity lasts and disease risk is reduced.