Efficacy and Safety of Ensitrelvir for Asymptomatic or Mild COVID‐19: An Exploratory Analysis of a Multicenter, Randomized, Phase 2b/3 Clinical Trial.

Background: This phase 2b/3, randomized, placebo‐controlled trial explored the efficacy and evaluated the safety of ensitrelvir. This trial involved individuals with asymptomatic infection with severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) and patients with mild symptoms of coronavirus disease 2019 (COVID‐19). Methods: The trial was conducted at 57 medical institutions in Japan, South Korea, and Vietnam (study period: January 6–August 14, 2022). Eligible participants were randomized (1:1:1) to the ensitrelvir 125‐mg, ensitrelvir 250‐mg, or placebo group, received the allocated intervention orally, and were followed up until Day 28. Participants self‐rated the severity of 14 typical COVID‐19 symptoms and recorded the data in an electronic diary. Results: In total, 572 participants (194, 189, and 189 in the ensitrelvir 125‐mg, ensitrelvir 250‐mg, and placebo groups, respectively) were included in the intention‐to‐treat population. Ensitrelvir 125‐mg group observed a 77% reduction in the risk of developing any of the 14 COVID‐19 symptoms or fever and a 29% reduction in the risk of worsening of such symptoms or fever versus placebo (statistically nonsignificant). The viral RNA, viral titer, and time to infectious viral clearance observed a statistically significant decrease versus placebo. Most treatment‐related adverse events (TEAEs) were mild to moderate in severity, and the most common TEAE observed across groups was a decrease in high‐density lipoprotein. Conclusions: Our exploratory results suggest a potential reduction in the risk of development or worsening of COVID‐19 symptoms with ensitrelvir. Ensitrelvir showed antiviral efficacy and was well tolerated. Trial Registration: Japan Registry of Clinical Trials identifier: jRCT2031210350. [ABSTRACT FROM AUTHOR]