The vaccination system exploits the memory of the immune system: a vaccine that produces memory cells is injected into the person to be immunized to make the body immune.
The vaccine is a preparation that resembles the pathogen because it contains antigens, that is, the same infectious agents that cause the disease (but rendered harmless to prevent them from being dangerous).
If we inject ourselves with a vaccine, our immune system recognizes it as foreign and within two to three weeks produces antibodies that neutralize it and specialized cells (T lymphocytes) that attack it. Thus, when we encounter the pathogen, our immune system reacts immediately, defending us from the disease.
Vaccines reduce risks of getting a disease by working with your body’s natural defenses to build protection. When you get a vaccine, your immune system responds. Immunization saves millions of lives every year.
Different from vaccine is serum, although they are often considered synonymous.
Serum is the fluid taken from blood, consisting of fibrinogen-free plasma, factor VIII, factor V, and prothrombin. To obtain fibrinogen-free plasma, coagulation is waited for after blood is drawn. Then the liquid part of the blood is separated from the corpuscular part and serum is obtained.
Serum also contains the antibodies we have produced in our repeated encounters with the various pathogens and vaccines encountered in our lives.