What is the difference between active and passive immunity?

Active immunity and passive immunity are fundamental concepts in immunology that describe how the body acquires protection against pathogens. The correct choice highlights a crucial distinction between the two.

Active immunity occurs when an individual's immune system is exposed to a specific antigen, prompting the body to generate a response. This exposure can happen through actual infection with a pathogen or via vaccination. As a result, the immune system produces its own antibodies and memory cells, leading to long-lasting immunity. This process requires time for the immune response to develop, but it results in a durable defense against future exposures to the same antigen.

On the other hand, passive immunity involves the transfer of pre-formed antibodies from one individual to another. This can happen naturally, such as when a mother passes antibodies to her baby through the placenta or breast milk, or artificially, through medical interventions like antibody infusions. Since the individual receiving the antibodies does not produce them on their own, this immunity is temporary and does not lead to the formation of memory cells.

Understanding this difference is essential for appreciating how vaccines work, the duration of immunity they provide, and the role of antibodies in immediate protection against certain diseases.