Challenge studies can be a powerful tool in the development of both therapeutic agents and vaccines. However, key decisions made in the study design process can have a profound impact on the outcome of the efficacy assessment. These include factors such as the selection criteria and screening of subjects as well as timing and frequency of the virological sampling and illness symptom data. A critical factor is selecting which efficacy endpoints to include and how precisely that is defined and calculated. While the principles of the endpoints are the same in challenge studies and field trials, subtle but vital differences in the endpoint definitions need to be made between the two clinical trial formats to account for the different context. Having access to large amounts of historical data can assist understanding of the natural variability and distribution of disease across the population, which is important for design of robust challenge studies.
