Shionogi has enrolled the first participant in Japan in its Phase III clinical trial of oral antiviral ensitrelvir to prevent symptomatic SARS-CoV-2 infection.

The global, placebo-controlled, double-blind, randomised study titled “Stopping COVID-19 pRogression with early Protease InhibitOr treatment – Post Exposure Prophylaxis (SCORPIO-PEP)" intends to enrol around 2,200 participants across Europe, South America, Africa, Asia, and North America.

Participants who were exposed to a household person with symptomatic Covid-19 and had a negative screening test for SARS-CoV-2 infection were enrolled in the study.

They will be randomised to receive either ensitrelvir or placebo in a 1:1 ratio.

The primary endpoint of the study is the proportion of participants infected with SARS-CoV-2 and display disease symptoms onset through day ten.

Shionogi CEO Isao Teshirogi said: “Part of managing Covid-19 in the longer term is identifying strategies to minimise the spread of the virus.

“This study will add further data to that obtained in the Phase III part of the pivotal SCORPIO-SR trial (Phase II/III study), conducted in Asia, which demonstrated that ensitrelvir can effectively treat patients with mild-to-moderate Covid-19, leading to a statistically significant reduction in the time it takes to resolve the typical Covid-19-related symptoms.”

Known as Xocova in Japan, ensitrelvir has received Ministry of Health, Labour and Welfare (MHLW) approval for emergency use. It is an investigational drug outside Japan.

Shionogi plans to enrol the first participant in the US this July.

The company has developed Ensitrelvir along with Hokkaido University. It selectively inhibits viral 3CL protease and suppresses the replication of SARS-CoV-2.