Which statement correctly describes acquired herd immunity?

• A. Acquired herd immunity is resistance due to age or breed
• B. Acquired herd immunity is universal and permanent
• C. Acquired herd immunity is resistance developed through protective immunity (natural or induced)
• D. Acquired herd immunity is the same as innate immunity

Answer: (C)

Acquired herd immunity comes from protective immunity that individuals develop after exposure or vaccination, involving the adaptive immune system with memory. When many people in a population become immune—whether from natural infection or vaccination—the spread of the pathogen slows, reducing transmission to those who are still susceptible. This collective protection depends on the immune system’s ability to recognize and remember the pathogen, not on inherent traits like age or breed.

It’s not resistance from age or breed, which are genetic or non-specific factors. It’s not guaranteed to be universal or permanent, since immunity can wane and pathogen dynamics or coverage can change over time. And it’s not the same as innate immunity, which is non-specific and lacks immunological memory.