Working of Vaccine in a Human Body: When a human body is vaccinated then preventive vaccine protect the individual by following steps 1. The vaccine introduces a small component or a non-harmful form of the pathogen into the body. This is called the foreign antigen. 2. The body’s immune system produces an immune response to the pathogen by generating antibodies, killer cells, or both. 3. A small group of “memory” B-cells and T-cells remain in the body and can quickly initiate a strong immune response, i.e. by producing antibodies, and helping the production of killer T-cells or antibodies, respectively. The next time the real pathogen is encountered, the immune system remembers it and mounts a much larger, quicker response than it would have if the individual had never received the vaccine. This is called “immune memory...