title: Novel Ordered Stepped-Wedge Cluster Trial Designs for Detecting Ebola Vaccine Efficacy Using a Spatially Structured Mathematical Model.
abstract: During the 2014 Ebola virus disease (EVD) outbreak, policy-makers were confronted with difficult decisions on how best to test the efficacy of EVD vaccines. On one hand, many were reluctant to withhold a vaccine that might prevent a fatal disease from study participants randomized to a control arm. On the other, regulatory bodies called for rigorous placebo-controlled trials to permit direct measurement of vaccine efficacy prior to approval of the products. A stepped-wedge cluster study (SWCT) was proposed as an alternative to a more traditional randomized controlled vaccine trial to address these concerns. Here, we propose novel "ordered stepped-wedge cluster trial" (OSWCT) designs to further mitigate tradeoffs between ethical concerns, logistics, and statistical rigor.
  
  
  
  We constructed a spatially structured mathematical model of the EVD outbreak in Sierra Leone. We used the output of this model to simulate and compare a series of stepped-wedge cluster vaccine studies. Our model reproduced the observed order of first case occurrence within districts of Sierra Leone. Depending on the infection risk within the trial population and the trial start dates, the statistical power to detect a vaccine efficacy of 90% varied from 14% to 32% for standard SWCT, and from 67% to 91% for OSWCTs for an alpha error of 5%. The model's projection of first case occurrence was robust to changes in disease natural history parameters.
  
  
  
  Ordering clusters in a step-wedge trial based on the cluster's underlying risk of infection as predicted by a spatial model can increase the statistical power of a SWCT. In the event of another hemorrhagic fever outbreak, implementation of our proposed OSWCT designs could improve statistical power when a step-wedge study is desirable based on either ethical concerns or logistical constraints.
authors: Department of Global Health and Social Medicine, Harvard Medical School, Boston, Massachusetts, United States of America.
authors: Ibrahim
authors: I
authors: Diakite
authors: Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, Massachusetts, United States of America.
authors: Eric Q
authors: EQ
authors: Mooring
authors: Division of Infectious Diseases, Brigham and Women's Hospital, Boston, Massachusetts, United States of America.|Division of Infectious Diseases, Massachusetts General Hospital, Boston, Massachusetts, United States of America.|Department of Medicine, Harvard Medical School, Boston, Massachusetts, United States of America.
authors: Gustavo E
authors: GE
authors: Velásquez
authors: Department of Global Health and Social Medicine, Harvard Medical School, Boston, Massachusetts, United States of America.|Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, Massachusetts, United States of America.|Division of Global Health Equity, Brigham and Women's Hospital, Boston, Massachusetts, United States of America.|Partners In Health, Boston, Massachusetts, United States of America.
authors: Megan B
authors: MB
authors: Murray
mesh_terms: D002986:Clinical Trials as Topic / Q000941:ethics / Q000331:legislation & jurisprudence / Q000379:methods*; D004196:Disease Outbreaks / Q000517:prevention & control*; D046129:Ebola Vaccines / Q000009:adverse effects* / Q000276:immunology*; D005544:Forecasting; D019142:Hemorrhagic Fever, Ebola / Q000453:epidemiology / Q000517:prevention & control* / Q000821:virology; D006801:Humans; D015233:Models, Statistical; D012807:Sierra Leone / Q000453:epidemiology
chemical_list: D046129:Ebola Vaccines