Box 1.

Explanation of the Use of a “Registrational Cohort”

What is a registrational cohort and what is its purpose? A registrational cohort is a pretrial stage during which participants are enrolled in a clinical study, but where no drugs are evaluated. Participants are tested regularly for HIV infection, which provides information on the baseline HIV incidence in the community where the study will take place. What are the advantages of a registration cohort? First, to identify, recruit, and follow-up a cohort of volunteers at risk of HIV who may be willing to participate in the trial. Second, to provide an estimate of the incidence of HIV in the community. This is crucial as it allows researchers to calculate the potential effect of PrEP in the trial. It is one method of calculating, what is known as a “counterfactual placebo.” Third, it allows researchers to understand people's knowledge, perceptions, uptake of, and adherence to PrEP (where it is available). Finally, to engage community in defining and refining key messages about HIV vaccines and PrEP, as well as developing tools to convey these messages.

Information from https://www.prepvacc.org/registration-cohort

PrEP, pre-exposure prophylaxis.