A Covid oral antiviral pill, developed by Japanese pharma company Shionogi & Co, has shown rapid clearance of a virus that causes Covid-19.

The pill, "S-217622 demonstrated rapid clearance of the infectious SARS-CoV-2 virus", the company said in a statement.

It added that the pill can be orally administered once - daily mainly in vaccinated patients, with no risk factors for severe complications, within five days of onset of Covid symptoms.

On day four of treatment (following the third dose), the proportion of patients with positive viral titer decreased by approximately 90 per cent versus placebo. The pill also shortened infectious virus shedding by 1-2 days versus placebo.

Further, "there was no significant difference in the total score of 12 Covid-19 symptoms between treatment arms", although the pill showed improvement in a composite score of five "respiratory and feverish" symptoms, the company said.

The clinical trials showed that S-217622 was well-tolerated, and no reports of serious adverse events.

"These results demonstrate that S-217622 rapidly eliminates SARS-CoV-2 in patients versus placebo, marking its potential, if approved, as an effective treatment option for Covid-19," said Isao Teshirogi, President and CEO at Shionogi, in a statement.

"As infections continue to rise in areas worldwide, it is important we have access to a range of easily administered treatment options to ease the pressures on our healthcare systems," Teshirogi added.