Final answer:
Vaccines protect humans from pathogens by creating memory B-cells and T-cells, which allow the immune system to quickly respond to subsequent exposures to the same pathogen. This mechanism establishes immunity, whereby the body can resist reinfection without developing symptoms.
Step-by-step explanation:
Vaccines help protect humans from pathogens by creating memory B-cells and T-cells before an individual actually encounters the pathogen and gets sick. When a person is vaccinated, their immune system is artificially exposed to an antigen, similar to what would happen during an actual infection, but without causing disease. As a response, the immune system produces antibodies and memory cells as if it had encountered the true pathogen. These memory cells include both memory B-cells and memory T-cells, which are crucial in the immune system's ability to remember and quickly respond to a pathogen if encountered again.
Memory B-cells have the specific role of retaining information about the pathogen, allowing for a faster and stronger immune response upon subsequent exposures. The rapid production of antibodies by these cells can prevent an infection from establishing itself, offering protection without the individual even realizing they have been re-exposed to the pathogen.