Passive immunity can be acquired through which of the following?

• A. Vaccination
• B. Infection
• C. Breath tests
• D. Breast milk transfer from mother to infant

Answer: (D)

Passive immunity involves obtaining antibodies from another source rather than making them in one’s own immune system. A key example is the transfer of maternal antibodies to a newborn through breast milk. Secretory antibodies in breast milk, especially IgA, line the infant’s mucosal surfaces and provide immediate protection, supplementing the baby’s defenses for a period after birth. Some maternal IgG also crosses the placenta during pregnancy, offering additional protection before birth. Both of these pathways deliver antibodies directly to the recipient without requiring the recipient’s immune system to actively respond, and the protection wanes over time as antibodies are cleared, without creating memory in the infant.

Vaccination and natural infection, in contrast, stimulate the recipient’s own immune response to produce antibodies and memory cells—this is active immunity. Breath tests do not confer immunity.