Japan's Shionogi & Co Ltd said on Wednesday its oral treatment for COVID-19 demonstrated a significant reduction in symptoms compared with a placebo in a Phase III trial in Asia.

The drug, a protease inhibitor known as ensitrelvir, met its primary endpoint in a trial conducted among predominantly vaccinated patients with mild to moderate cases of COVID-19, the company said in a statement.

Shionogi's shares reversed an early decline after the announcement, closing 1.1% higher in Tokyo versus a 1.5 drop in the benchmark Nikkei gauge.

Ensitrelvir met the trial's goal in reducing five key symptoms of the omicron variant of COVID-19 within 72 hours of onset, the company said.

Regulatory authorities in Japan previously denied emergency approval for use of the pill, saying they wanted to see more data on its effectiveness. There are also concerns the drug could pose risk to pregnancies, based on results from animal studies.

Shionogi said it has shared top-line data from the Phase III study with Japanese regulators as part of deliberations on approval of the drug.

Shionogi has global aspirations for the drug, also known as S-217622 and by the brand name Xocova, which would compete with COVID-19 pills from Pfizer Inc and Merck & Co Inc that have already been approved in Japan and elsewhere.

The company has signed an agreement to sell about a million doses to the government, pending the drug's approval.

Chief Executive Isao Teshirogi has said annual production of the drug could reach 10 million doses. The firm has received U.S. government support for a global Phase III trial.