
2.1. Study design
This is a multicenter, randomized, double-blind, placebo-controlled, phase 3 study to test the efficacy and safety of ensitrelvir in patients with mild-to-moderate COVID-19. The study will be conducted across several sites in Japan, Korea, Singapore, and Vietnam beginning in February 2022 and has been registered in the Japan Registry of Clinical Trials: jRCT2031210350. Patients will be randomized into 3 arms—ensitrelvir 125 mg, ensitrelvir 250 mg, and placebo. The intervention period will span 5 days (Days 1–5), during which patients will be administered ensitrelvir or placebo, followed by a follow-up period of 23 days (Days 6–28; Fig. Study design. 