ELANCO Advanced Animal Science Practice Exam 2026 - Free Animal Science Practice Questions and Study Guide

Vaccines work by training the immune system to recognize a pathogen and respond more rapidly if encountered again, which creates active immunity through the adaptive immune response. When enough individuals develop this kind of immunity, the spread of the disease slows or stops in the population, helping protect those who aren’t immune—this is herd immunity. Active immunity involves the body’s own B and T cells forming a targeted response and memory, so protection lasts for years or a lifetime. In contrast, passive immunity is immediate but temporary, coming from antibodies produced outside the recipient (for example, maternal antibodies transferred to offspring); the recipient’s immune system isn’t primed to respond on its own.

The correct statement reflects that vaccines induce adaptive, active immunity and that herd immunity depends on a sufficient proportion of the population being immune to reduce transmission. The other options mix up how immunity is generated and the timing of protection: vaccines do not primarily elicit passive immunity from a dam, active immunity is not immediate at birth, and herd immunity does not require every individual to be immune—only a protective threshold.