11.2.4—Types of immunity

Active immunity is protection made by the person’s own immune response after an antigen is encountered. Passive immunity is protection supplied by antibodies made elsewhere, so the recipient’s immune system is not the source of those antibodies.

• Active — natural: Exposure to a pathogen provides the antigen; the person produces antibodies and memory cells. Protection takes time to build, but memory can support a faster, stronger response to the same antigen later.
• Active — artificial: A vaccination provides antigenic stimulation without requiring the person to first develop the disease; the person produces antibodies and memory cells. The specific vaccination process is covered in the following objectives.
• Passive — natural: Ready-made antibodies pass from another person, such as across the placenta or in colostrum. Protection is available without the recipient making the antibodies, but no memory cells are formed.
• Passive — artificial: Ready-made antibodies are injected or infused, for example an antitoxin when rapid protection is needed. Antibodies are available promptly, but the recipient does not form memory cells and may need another antibody supply after reinfection.

The key distinction is who makes the antibodies. Own production in active immunity explains the slower primary response and the presence of memory cells; supplied antibodies in passive immunity explain the immediate protection but the absence of a memory-based secondary response.

Active does not mean immediate, and passive does not create immunological memory. Natural versus artificial describes how the immunity is acquired; active versus passive describes whether the recipient makes the antibodies. This card does not give the detailed steps of vaccination or disease-control programmes.