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Herd immunity, vaccination and moral obligation
  1. Matthew Bullen1,
  2. George S Heriot2,
  3. Euzebiusz Jamrozik3,4,5
  1. 1 Box Hill Hospital, Eastern Health, Melbourne, Victoria, Australia
  2. 2 Department of Infectious Diseases, Melbourne Medical School, University of Melbourne, Melbourne, Victoria, Australia
  3. 3 Ethox Centre and Pandemic Sciences Institute, University of Oxford, Oxford, UK
  4. 4 Royal Melbourne Hospital Department of Medicine, University of Melbourne, Melbourne, Victoria, Australia
  5. 5 Monash Bioethics Centre, Monash University, Melbourne, Victoria, Australia
  1. Correspondence to Dr Euzebiusz Jamrozik, Ethox Centre, University of Oxford, Oxford OX3 7LF, UK; euzebiusz.jamrozik{at}ethox.ox.ac.uk

Abstract

The public health benefits of herd immunity are often used as the justification for coercive vaccine policies. Yet, ‘herd immunity’ as a term has multiple referents, which can result in ambiguity, including regarding its role in ethical arguments. The term ‘herd immunity’ can refer to (1) the herd immunity threshold, at which models predict the decline of an epidemic; (2) the percentage of a population with immunity, whether it exceeds a given threshold or not; and/or (3) the indirect benefit afforded by collective immunity to those who are less immune. Moreover, the accumulation of immune individuals in a population can lead to two different outcomes: elimination (for measles, smallpox, etc) or endemic equilibrium (for COVID-19, influenza, etc). We argue that the strength of a moral obligation for individuals to contribute to herd immunity through vaccination, and by extension the acceptability of coercion, will depend on how ‘herd immunity’ is interpreted as well as facts about a given disease or vaccine. Among other things, not all uses of ‘herd immunity’ are equally valid for all pathogens. The optimal conditions for herd immunity threshold effects, as illustrated by measles, notably do not apply to the many pathogens for which reinfections are ubiquitous (due to waning immunity and/or antigenic variation). For such pathogens, including SARS-CoV-2, mass vaccination can only be expected to delay rather than prevent new infections, in which case the obligation to contribute to herd immunity is much weaker, and coercive policies less justifiable.

  • Ethics
  • Policy
  • Public Policy
  • COVID-19
  • Epidemiology

Data availability statement

Data sharing not applicable as no data sets generated and/or analysed for this study.

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Data availability statement

Data sharing not applicable as no data sets generated and/or analysed for this study.

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Footnotes

  • Contributors All authors listed contributed to the planning and writing of the submitted manuscript. EJ is the senior author and overall guarantor of the publication.

  • Funding This research was funded in whole, or in part, by Wellcome Trust (203132 and 221719). The Trust and Confidence research programme at the Pandemic Sciences Institute at the University of Oxford is supported by an award from the Moh Foundation.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.