Immunisation for the Sake of the ‘Herd’

Abstract

Individuals who vaccinate directly benefit from the protection it affords them against contracting a specific disease. However, others will often also benefit, as vaccinated individuals cannot transmit the disease. Herd immunity refers to the indirect protection against infectious disease that unvaccinated, or nonimmune, individuals receive as a result of reduced disease transmission due to the presence of vaccinated, or immune, individuals. Herd immunity is important, particularly for individuals who cannot be vaccinated because of age or contraindications, who do not get vaccinated because of refusal, those for whom immunisation is ineffective or for whom immunity has waned due to age. Even when vaccination coverage in a given population is high, certain communities may be at risk of outbreaks if significant numbers of people choose not to vaccinate. Therefore, vaccine hesitancy and vaccine refusal threaten herd immunity. Policymakers can use vaccine mandates to increase vaccination coverage to promote herd immunity.

Key Concepts

  • Herd immunity refers to the indirect protection against infectious disease that unvaccinated, or nonimmune, individuals receive as a result of reduced disease transmission due to the presence of vaccinated, or immune, individuals.
  • Herd immunity can provide protection for individuals who cannot be vaccinated because of age or contraindications, who do not get vaccinated because of refusal or other reasons and for those whom vaccination is ineffective.
  • Even if vaccination coverage in a population is high, vaccines are not perfect, so certain communities may be at risk for outbreaks of infectious disease if the vaccination coverage dips below the herd immunity threshold, such that disease transmission can take place.
  • Although some individuals may be tempted to forego immunisation, believing they are protected by the vaccination of others around them (herd immunity), nonvaccinated individuals are at higher risk for contracting infectious diseases. For certain diseases, the severity of illness may be increased if contracted at an older age due to delayed exposure (herd severity effect).
  • Public support of vaccination programmes, such as the National Vaccine Injury Compensation Program in the United States, is justified at least partially because vaccination at the individual level indirectly benefits the health of the population at large.

Keywords: herd immunity; immunisation; herd immunity threshold; reproduction number; vaccine hesitancy; vaccine refusal; vaccine mandates; vaccination coverage; herd severity effect

Figure 1. Educational graphic demonstrating benefits of herd immunity. Courtesy of the United States Centers for Disease Control and Prevention (CDC) 2017.
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Further Reading

PlotkinSA, OrensteinW and OffitPA (eds) (2017) Plotkin's Vaccines, 7th, 1720 pp edn. Philadelphia, PA: W.B. Saunders Co. (Elsevier).

SchwartzJL and CaplanAL (eds) (2017) Vaccination Ethics and Policy: An Introduction with Readings, 432 pp. Cambridge, MA: MIT Press.

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How to Cite close
Chapman, Carolyn R, and Caplan, Arthur L(Mar 2018) Immunisation for the Sake of the ‘Herd’. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0027995]