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Do coronavirus vaccine challenge trials have a distinctive generalisability problem?
  1. Nir Eyal1,
  2. Tobias Gerhard2
  1. 1 Center for Population-Level Bioethics, Department of Philosophy (SAS) and Department of HBSP (SPH), Rutgers University, New Brunswick, New Jersey, USA
  2. 2 Center for Pharmacoepidemiology and Treatment Science and Ernest Mario School of Pharmacy, Rutgers University, New Brunswick, New Jersey, USA
  1. Correspondence to Professor Nir Eyal, Center for Population-Level Bioethics, Dept of Philosophy (SAS) and Dept of HBSP (SPH), Rutgers University, New Brunswick, New Jersey, USA; nir.eyal{at}


Notwithstanding the success of conventional field trials for vaccines against COVID-19, human challenge trials (HCTs) that could obtain more information about these and about other vaccines and further strategies against it are about to start in the UK. One critique of COVID-19 HCTs is their distinct paucity of information on crucial population groups. For safety reasons, these HCTs will exclude candidate participants of advanced age or with comorbidities that worsen COVID-19, yet a vaccine should (perhaps especially) protect such populations. We turn this cliché on its head. The truth is that either an HCT or a field trial has intrinsic generalisability limitations, that an HCT can expedite protection of high-risk participants even without challenging them with the virus, and that an important route to obtaining results generalisable to high-risk groups under either strategy is facilitated by HCTs.

  • biostatistics
  • clinical trials
  • COVID-19
  • ethics
  • research ethics

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  • Contributors Both authors contributed equally.

  • Funding NE receives funding from the US National Science Foundation, Award # 2039320 and from Open Philanthropy.

  • Competing interests NE serves on the Board of Advisor of 1DaySooner, an unpaid position.

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

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