Article Text

Download PDFPDF
Deciphering assumptions about stepped wedge designs: the case of Ebola vaccine research
  1. Adélaïde Doussau,
  2. Christine Grady
  1. Department of Bioethics, Clinical Center, National Institutes of Health, Bethesda, Maryland, USA
  1. Correspondence to Dr Adélaïde Doussau, Department of Bioethics, Clinical Center, National Institutes of Health, 10 Center Drive, Building 10/1C118, Bethesda, MD 20892-1156 USA; doussau2.adelaide{at}


Ethical concerns about randomising persons to a no-treatment arm in the context of Ebola epidemic led to consideration of alternative designs. The stepped wedge (SW) design, in which participants or clusters are randomised to receive an intervention at different time points, gained popularity. Common arguments in favour of using this design are (1) when an intervention is likely to do more good than harm, (2) all participants should receive the experimental intervention at some time point during the study and (3) the design might be preferable for practical reasons. We examine these assumptions when considering Ebola vaccine research. First, based on the claim that a stepped wedge design is indicated when it is likely that the intervention will do more good than harm, we reviewed published and ongoing SW trials to explore previous use of this design to test experimental drugs or vaccines, and found that SW design has never been used for trials of experimental drugs or vaccines. Given that Ebola vaccines were all experimental with no prior efficacy data, the use of a stepped wedge design would have been unprecedented. Second, we show that it is rarely true that all participants receive the intervention in SW studies, but rather, depending on certain design features, all clusters receive the intervention. Third, we explore whether the SW design is appealing for feasibility reasons and point out that there is significant complexity. In the setting of the Ebola epidemic, spatiotemporal variation may have posed problematic challenges to a stepped wedge design for vaccine research. Finally, we propose a set of points to consider for scientific reviewers and ethics committees regarding proposals for SW designs.

  • Research Ethics
  • Clinical trials
  • Policy Guidelines/Inst. Review Boards/Review Cttes.
  • Biostatistics
  • Drugs and Drug Industry

Statistics from

Request Permissions

If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.


  • Contributors AD and CG both contributed to the design of the study. AD did the review of the literature, extracted the data from the literature and the trial registries. AD and CG independently reviewed the eligible studies to select the drug/vaccines studies. Both extracted independently the data of the drug/vaccines studies. AD first drafted the manuscript. Both authors contributed to the final version and validated the manuscript.

  • Disclaimer The views expressed are those of the authors and do not necessarily reflect those of the Clinical Center, the National Institutes of Health, the Public Health Service or the Department of Health and Human Services.

  • Competing interests None declared.

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

  • Data sharing statement The list of stepped wedge studies collected through the registries search is accessible to researchers by contacting the first author.

Other content recommended for you