PRACT feasibility study design
UC
PRACT is a three-stage single-blind parallel adaptive randomized controlled trial. Stage 1 compares usual care (UC) to PPKAY or PPKAY with standard booster through a 1:1:1 allocation with a 12-block randomization. Stage 2 removes the usual care arm but continues enrollment in the other two arms at a 1:1 allocation with a 12-block randomization. Stage 3 continues the most effective arm from Stage 2 and allocates additional participants into the most effective arm and a new arm—PPKAY with a personalized booster. Additional participants are to be enrolled at a 1:4 allocation with 12-block randomization into the Stage 3 intervention arms. This adaptive method allows us to answer multiple successive questions with streamlined enrollment and processes; thus enrolling fewer patients in the fully powered trial than if we used three successive clinical trials. While for the future PRACT, all adaptations are planned to reach predetermined significance through interim analyses, the adaptations for this feasibility trial were triggered by enrollment numbers determined 