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Wrong question and the wrong standard of proof
  1. Marc Lipsitch
  1. Center for Communicable Disease Dynamics, Harvard School of Public Health, Boston, Massachusetts, USA
  1. Correspondence to Professor Marc Lipsitch, Center for Communicable Disease Dynamics, Harvard School of Public Health, Boston, Massachusetts, USA; mlipsitc{at}

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I have two concerns about Pugh et al’s case that vaccine requirements without a natural immunity exception are unjustified.1 First, the scientific question they suggest must be answered to justify the policy is in my view the wrong one, or at least not the only relevant one. Second, the authors set up a standard for public health regulation that will be often (and specifically in this case) unattainable, risking paralysis of public health authorities.

Pugh et al suggest two legitimate bases for vaccine mandates: ‘the prevention of severe outcomes from COVID-19 and the reduction of viral transmission.’ Governments and employers have a legitimate interest in protecting the health of their citizens and workers, respectively. To maximally accomplish these goals, the relevant scientific question for whether people with prior infection should be subject to a vaccine mandate is: in persons who have been previously infected, does vaccination enhances protection against severe disease and/or infection and transmission? The relevant comparison, if one is trying to maximise protection in the population, is not vaccination vs prior infection, but (vaccination plus prior infection) vs prior infection alone. I am unaware of a systematic review of this question, but the answer in two recent studies appears to be that the combination is more protective(though see below for caveats in interpreting such studies).2 ,3 The comparison the authors propose, in contrast, seems to be one based on an unstated conception of fairness and adequacy: if vaccination alone provides some level of protection, and prior infection can’t be shown to provide an inferior level, then prior infection should be an acceptable alternative to vaccination to satisfy mandates. No argument is given to support the greater relevance of the comparison the authors emphasise.

A second and independent concern is that the authors’ proposal …

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  • Correction notice Since this article was first published, a set of competing interests have been added for the author.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests The author reports honoraria/consulting from Merck, Sanofi-Pasteur, Bristol Myers-Squibb, and Antigen Discovery; research funding (institutional) from Pfizer; and unpaid scientific advisory services to Janssen, Astra-Zeneca, One Day Sooner, and Covaxx (United Biomedical). He is on the Scientific Advisory Committee for CEPI, the Coalition for Epidemic Preparedmess Innovations. He is also affiliated with the US Centers for Disease Control and Prevention through an Intergovernmental Personnel Agreement with Harvard University. This article reflects his personal views and is written purely in his academic capacity, not reflecting the views of any organization or government agency.

  • Provenance and peer review Commissioned; internally peer reviewed.

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