22.1 In Focus: Ring Trial Design

This focus article explains the origins, design, and rationale behind the ring trial design for clinical medical countermeasure (MCM) research, especially in an emergency response setting. In a ring trial, individuals linked to a newly diagnosed infectious disease case are recruited and randomized as a cluster or individually within the ring to an intervention such as vaccination or a control arm. The advantages and disadvantages of the ring trial design are outlined, and the Ebola ça Suffit! vaccine ring trial in Guinea is provided as an illustration. Considerations for an appropriate study design and potential modifications to the design, such as amending the definition of a ring, are described. The ring trial design has great potential for future applications to evaluate fast-acting interventions in settings where spatiotemporal disease incidence is highly unpredictable and infection is relatively rare. Such an approach has the potential to accelerate the accrual of critical results in emergency response research.