Final answer:
Natural passive immunity is the transfer of antibodies from mother to infant during pregnancy via the placenta and through breastfeeding, providing temporary protective immunity without the infant's active immune response.
Step-by-step explanation:
The type of immunization that occurs when antibodies pass from mother to infant during breastfeeding or through the placenta during pregnancy is known as natural passive immunity. This form of immunity is crucial for the protection of infants who are not yet capable of mounting their own immune responses. Natural passive immunity provides immediate, but temporary, protection to the infant. For example, the IgG antibody class is the only one able to traverse the placenta from the mother's blood into the fetal bloodstream, conferring immunity to the infant for up to six months post-birth. Similarly, Secretory IgA antibodies are transferred through breast milk, offering additional protection against pathogens.
In contrast to active immunity, where the body's own immune system actively produces antibodies in response to an infection or vaccine, passive immunity does not lead to the development of immunological memory, meaning that the protection it offers is not long-lasting. Instead, once the transferred antibodies degrade, the protection they provide disappears.