What is herd immunity?

Herd immunity refers to the concept that when a significant portion of a population is vaccinated against a contagious disease, it reduces the overall amount of the virus or bacteria that can spread in the community. This means that even individuals who are not vaccinated, such as those who cannot receive vaccines for medical reasons or those who may not respond adequately to vaccination, are indirectly protected because the spread of the disease is minimized.

Achieving herd immunity is crucial in controlling outbreaks and protecting vulnerable populations. Vaccination not only protects the person who receives the vaccine but also contributes to a safer environment for everyone, thus breaking the chain of transmission.

The other choices describe various aspects of immunity and immune responses but do not encapsulate the essence of herd immunity as effectively. Immunity from infection or prior exposure refers to individual protection, while the acquired immune response relates specifically to immune reactions from vaccines, which do not necessarily imply community-level protection. Therefore, the choice that describes herd immunity accurately is the one that focuses on the vaccination of a significant portion of the population.