What Is the Difference Between Active and Passive Immunity?
Learn the difference between active and passive immunity for AQA A Level Biology, including sources, antibodies, memory cells and exam-focused examples.
Active immunity develops when your own immune system produces antibodies and memory cells after exposure to an antigen. Passive immunity occurs when ready-made antibodies are transferred to you from another source. The main differences are how antibodies are obtained, how long protection lasts and whether memory cells form.
Active immunity
In active immunity, an antigen stimulates a specific immune response. B lymphocytes undergo clonal selection and produce plasma cells, which release antibodies. Some B lymphocytes become memory cells. If the same antigen enters the body again, the memory cells produce a faster and larger secondary immune response.
Active immunity can be:
- Naturally acquired, such as after recovering from an infection.
- Artificially acquired, such as after vaccination. A vaccine contains antigens that stimulate an immune response without causing the disease in the usual way.
Active immunity usually develops relatively slowly, but it is often long-lasting because memory cells remain.
Passive immunity
In passive immunity, antibodies made by another individual are transferred to the person. The recipient does not produce the antibodies through their own primary immune response, so memory cells are not formed.
Passive immunity can be:
- Naturally acquired, when antibodies pass from mother to baby across the placenta or in breast milk.
- Artificially acquired, when an injection containing antibodies is given, such as antiserum after exposure to a toxin.
Protection from passive immunity is immediate, but it is temporary because the antibodies are gradually broken down. It does not produce a secondary immune response in the recipient.
Key exam distinction
A common mistake is to describe vaccination as passive immunity. Vaccination gives active artificial immunity because vaccine antigens stimulate the person’s own B lymphocytes to produce antibodies and memory cells. An injection of antibodies gives passive artificial immunity because the antibodies are supplied ready-made.
A useful summary is: active immunity makes antibodies and memory cells; passive immunity receives antibodies but does not make memory cells.
