Ashby B & Best A (2021) Herd immunity. Curr. Biol. 31:R174-R177.
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Herd immunity is an important yet often misunderstood concept in epidemiology. As immunity accumulates in a population—naturally during the course of an epidemic or through vaccination—the spread of an infectious disease is limited by the depletion of susceptible hosts. If a sufficient proportion of the population is immune—above the ‘herd immunity threshold’—then transmission generally cannot be sustained. Maintaining herd immunity is therefore critical to long-term disease control. In this primer, we discuss the concept of herd immunity from first principles, clarify common misconceptions, and consider the implications for disease control.