What is herd immunity?

Herd immunity refers to the concept where a sufficient percentage of a population becomes immune to a disease, either through vaccination or previous infections, thereby providing indirect protection to individuals who are not immune. When a critical proportion of the population is immune, the spread of the disease is curtailed, reducing the likelihood that individuals who cannot be vaccinated—such as those with certain medical conditions or allergies—will contract the disease. This phenomenon is crucial in controlling infectious diseases and ensuring public health safety.

The other options do not accurately define herd immunity. While medical treatments can protect individuals, they do not encompass the collective protection that immunity provides to a community. Resistance to diseases among elderly populations highlights a specific demographic's health but does not represent the broader principle of herd immunity. Lastly, temporary immunity gained after an illness pertains to individual immunity rather than the community-wide effect essential for herd immunity.