Definition & Meaning of "herd immunity"

What is "herd immunity"?

Herd immunity refers to a situation where a large portion of a population becomes immune to a disease, either through vaccination or previous infection, providing indirect protection to those who are not immune. When enough people in a community are immune to a disease, it becomes more difficult for the disease to spread from person to person. Herd immunity is important for protecting vulnerable individuals who cannot receive vaccines because of medical reasons or age, such as newborns or individuals with certain medical conditions. The level of immunity needed to achieve herd immunity depends on the contagiousness of the disease and varies from one disease to another.