Trials within Cohorts (TwiCs)

Innovative Trial Design: Overcoming some of the problems common to traditional Randomized Clinical Trials

Trials within Cohorts (TwiCs) are a randomized trial design in which a trial is set up and conducted within an existing or newly started cohort. In a cohort that uses the TwiCs approach a group of participants with a particular condition of interest may agree to regular data collection and observation – and to random assignment into a future intervention. Once an intervention is trialed, only the cohort participants who have been assigned to the intervention group will be informed of their role as the trial group and an additional consent will be obtained. The control group receives the standard treatment according to the cohort procedures. Because of the multi-staged consent process, which differs from classic randomized controlled trials, TwiCs may better mimic clinical practice and improve recruitment of study participants. However, TwiCs-specific ethical, statistical and methodological challenges need to be addressed.

Since Juli 2024 we are implementing the TwiCs in the main centers of the Swiss HIV Cohort Study (SHCS). The SHCS, established in 1988 is a multicenter, prospective, nationwide, observational cohort study with around 10’000 active participants.

In parallel, we have implemented the TwiCs design in the ComBaCaL cohort, a large-scale general population-based cohort in two districts of Lesotho, in Southern Africa. Using the design, we evaluate several community-led decentralised models of care for hypertension, diabetes and HIV.