Which characteristic describes passive immunity?

Passive immunity is characterized by its transient nature, meaning it is generally short-lived. This type of immunity occurs when a person receives preformed antibodies rather than producing their own in response to an infection or vaccination. Because the immune system of the individual is not actively generating these antibodies, the effects do not last long, often only providing protection for a few weeks to months, depending on the source of the antibodies.

For example, maternal antibodies transferred to a baby through the placenta or through breast milk illustrate passive immunity. These antibodies provide immediate, but temporary, protection against infections during the early months of life. Over time, as the child's own immune system begins to develop and produce its own antibodies, the passive immunity wanes.

The other characteristics do not apply to passive immunity: it is not long-lasting since it relies on external sources for antibodies, it is not always actively developed as it does not involve an active immune response by the recipient, and it certainly involves antibodies because passive immunity is fundamentally based on the transfer and introduction of these pre-formed antibodies into the individual’s system.