Which best describes passive immunity?

• A. It is another term for innate immunity.
• B. It is acquired as a result of vaccination.
• C. It is mostly helpful as therapy for existing infections.
• D. It results from receiving pre-formed antibodies.

Answer: (D)

Passive immunity is the transfer of ready-made antibodies from one individual to another, providing immediate protection that is temporary and does not require the recipient’s immune system to create antibodies. This can happen when maternal antibodies pass through the placenta or are present in breast milk, or when immunoglobulin preparations are given directly to someone. The key idea is that the antibodies are pre-formed and simply transferred, rather than the recipient actively producing them in response to exposure. This is different from innate immunity, which is nonspecific and present from birth, and from active immunity, where the person’s own immune system generates antibodies after infection or vaccination.