Pre-proof of Herd immunity Journal

Journal Pre-proof

Herd immunity

Ben Ashby, Alex Best

PII: S0960-9822(21)00039-7


Reference: CURBIO 17181

To appear in Current Biology

Please cite this article as Ashby B, Best A, Herd immunity, Current Biology (2021), DOI: HTTPS://

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© 2021 Elsevier Inc.


Herd immunity

Ben Ashby1,* and Alex Best2

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 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.

What is herd immunity?

The notion of herd immunity is simple, yet profound: not every member of a population must be immune to prevent large-scale outbreaks, nor will everyone be infected during the course of an epidemic (Figure 1). It is both a fundamental epidemiological concept describing a natural phenomenon and a practical goal for long-term disease control, most commonly associated with vaccination programs.

Recently, during the COVID-19 pandemic, the subject of herd immunity — specifically, how and when it might be achieved — has received considerable attention from scientists, policymakers, and the general public.

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