Which of the following is an example of naturally acquired passive immunity?

• A. Antibodies are from mother to fetus
• B. Vaccination
• C. The body makes antibodies
• D. Injecting antibiotics

Answer: (A)

Naturally acquired passive immunity is protection conferred by antibodies that come from another person rather than being made by the recipient. An example is antibodies transferred from mother to fetus across the placenta, primarily IgG, which gives the newborn immediate protection at birth. This protection is temporary because maternal antibodies wane over weeks to months, and the infant will need to produce its own antibodies later. The body making antibodies is active immunity, and vaccination is an artificial way to stimulate that response—also not passive. Injecting antibiotics has no role in immunity, as it is a drug treatment, not antibody transfer.