[12] The Japanese government is reportedly considering allowing Shionogi permission to apply for approval for medical use before the final steps of trials are completed, potentially speeding up the release for sale.

This conditional early approval system has previously been used in Japan to accelerate the progression to market of other antiviral drugs targeting COVID-19, including remdesivir and molnupiravir.

[20][21] The SCORPIO-PEP trial, a global Phase 3 study, assessed the safety and efficacy of ensitrelvir in preventing symptomatic COVID-19 among household contacts of individuals with confirmed SARS-CoV-2 infection.

[21][22][23][24] Top-line results from this trial suggested that use of ensitrelvir as post-exposure prophylaxis may significantly reduce the risk of symptomatic COVID-19 infection in exposed household contacts compared to placebo.

[30] In May 2024, Shionogi announced that in a phase 3 trial (SCORPIO-HR), ensitrelvir did not achieve its primary endpoint of a statistically significant reduction in the time to sustained resolution of 15 common COVID-19 symptoms compared to placebo.