What does the term "herd immunity" refer to?

Herd immunity refers to a situation in which a significant portion of a population becomes immune to an infectious disease, either through vaccination or previous infections. This level of immunity within a community makes it less likely for the disease to spread, effectively protecting individuals who are not immune, such as those who cannot be vaccinated for medical reasons or those for whom the vaccine may not provide sufficient protection. When a large percentage of the population is vaccinated, the chain of transmission is disrupted, thereby contributing to the overall health of the community.

While individual vaccination efforts are important, herd immunity emphasizes the collective impact of vaccination on the population as a whole. It does not solely focus on the immunity developed through natural infections; rather, it underscores the importance of preventing disease spread through proactive vaccination strategies. Additionally, herd immunity is a concept applicable to both human and animal populations, so it is not limited to phenomena that occur only in animals. Thus, the correct answer highlights the significance of a large proportion of the population being vaccinated to establish herd immunity and protect the entire community.