What does "herd immunity" refer to?

Herd immunity refers to the phenomenon where a significant portion of a population becomes immune to a disease, primarily through vaccination. This immunity provides indirect protection to unvaccinated individuals because the spread of the disease is minimized. When a large percentage of the population is vaccinated, there are fewer opportunities for the disease to spread, thus protecting those who cannot be vaccinated due to medical reasons, age, or other factors.

This concept emphasizes the importance of widespread vaccination not only for individual health but also for community health, as it helps prevent outbreaks and contributes to the overall control of infectious diseases. The effectiveness of herd immunity works best when vaccination rates are high, as it significantly reduces the likelihood of disease transmission.