Artificial immunization against foreign agent when person is healthy prevents future infection. Immunization uses vaccines , substances that contain antigens to which immune system can respond. Genetically engineered bacteria can produce just the surface protein of a microbe. Several vaccines can be produced for a combination vaccination, utilizing surface proteins from several disease agents. Provides longer lasting protection.
Primary response is gradual.
It takes several days before antibodies appear. Antibody titer is amount of antibody present in serum. Titer slowly rises, evens off, then falls as antibodies bind to antigen or break down. More plasma and memory cells are present to produce antibodies rapidly. Active immunity lasts as long as clones of memory B and memory T cells are present.