How does active immunity differ from passive immunity?

Active immunity is characterized by the body's immune system engaging in a response to an antigen, which involves the production of antibodies and memory cells that can persist for years or even a lifetime. This type of immunity typically develops after exposure to an infectious agent, either through infection or vaccination. As a result, the immune system learns to recognize the antigen and mount a defense if exposed again in the future.

In contrast, passive immunity occurs when antibodies are transferred from one individual to another, providing immediate but temporary protection. This can happen, for example, when a mother passes antibodies to her newborn through breast milk or during pregnancy. Because the recipient's immune system does not create its own antibodies in this case, the duration of passive immunity is limited, generally lasting only a few weeks to months.

The distinction highlights that while active immunity develops as a result of an immune response and is more durable, passive immunity is an immediate but short-lived transfer of pre-formed antibodies from another source. This fundamental difference is crucial for understanding how the body protects itself against pathogens.