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◉ Science·1 min·Updated Mar 14, 2026

What is Herd Immunity?

Herd Immunity

Quick Answer

Herd immunity is a form of protection from infectious diseases that occurs when a large percentage of a population becomes immune, either through vaccination or previous infections. This reduces the spread of the disease, protecting those who are not immune.

Overview

Herd immunity is an important concept in public health and biology. It happens when enough people in a community become immune to a disease, making it harder for the disease to spread. This immunity can come from vaccinations or from people recovering from the disease itself. When a significant portion of the population is immune, even those who are not vaccinated, such as infants or those with certain health conditions, are better protected. For example, during the COVID-19 pandemic, widespread vaccination efforts aimed to achieve herd immunity to reduce the virus's transmission. The more people who are vaccinated, the less opportunity the virus has to spread, which helps to protect vulnerable individuals. Understanding herd immunity is crucial because it highlights the importance of vaccinations and collective health efforts in controlling infectious diseases.

Frequently Asked Questions

Herd immunity is achieved when a large portion of the population becomes immune to a disease, usually through vaccination. The specific percentage needed for herd immunity varies by disease, but it often requires a significant majority of the population to be immune.
Herd immunity is important because it helps protect those who cannot be vaccinated, such as people with certain medical conditions or allergies. When enough people are immune, the spread of the disease is slowed or stopped, reducing the chance of outbreaks.
Herd immunity can be harmful if it leads to complacency about vaccinations, resulting in lower vaccination rates. This can allow diseases to spread more easily, putting vulnerable populations at risk and potentially leading to outbreaks.