The United States on Wednesday authorised Pfizer Inc's antiviral Covid-19 pill for people ages 12 and older at risk of severe illness, the first oral and at-home treatment as well as a new tool against the fast-spreading Omicron variant.

Pfizer's antiviral regimen, Paxlovid, was nearly 90 percent effective in preventing hospitalisations and deaths in patients at high risk of severe illness, according to data from the company's clinical trial. Recent lab data suggests the drug retains its effectiveness against Omicron, Pfizer said.