What is the difference between active and passive immunity, with examples relevant to clinical practice?

• A. Active immunity arises from the patient’s own response to infection or vaccination; passive immunity comes from transferred antibodies such as maternal IgG or monoclonal antibodies
• B. Active immunity is inherited; passive immunity arises from vaccination
• C. Active immunity is immediate while passive takes time
• D. Passive immunity is produced by the patient’s own immune response

Answer: (A)

The key idea is how protection is acquired and how long it lasts. Active immunity happens when the person’s own immune system responds to an antigen, such as through infection or vaccination, and develops memory B and T cells. This memory allows a faster, stronger response upon re-exposure and tends to be long-lasting. For example, after vaccination, the body generates specific antibodies and memory cells that protect for years or decades.

Passive immunity provides immediate protection through antibodies that come from another source, not from the person’s own immune response. There’s no memory formed in the recipient, so once the transferred antibodies wane, protection ends. In clinical practice, this is seen with maternal IgG crossing the placenta to protect the newborn, or antibodies present in breast milk, which give short-term mucosal protection. Therapeutically, immune globulins or monoclonal antibodies (such as antibodies given after exposure to certain infections or to prevent disease in high-risk individuals) provide immediate, but temporary, protection without the recipient’s immune system generating its own response.

So, active immunity is a self-generated, memory-producing response to infection or vaccination; passive immunity is the transfer of antibodies from another source, providing immediate but non–memory-based protection.