Drugmaker Pfizer has said its Covid-19 anti-viral pill showed near 90 per cent efficacy in preventing hospitalisations and deaths in high-risk patients.
Recent lab data also suggests the drug retains its effectiveness against the fast spreading Omicron variant.
Last month, Pfizer said the oral medicine was around 89 per cent effective in preventing hospitalisations or deaths when compared to a placebo, based on interim results in around 1,200 people. Data from its final analysis of the trial disclosed on Tuesday includes an additional 1,000 people.
Nobody in the trial who received the Pfizer treatment died, compared with 12 deaths among placebo recipients.
The Pfizer pills are taken with the older anti-viral, Ritonavir every 12 hours for five days, beginning shortly after onset of symptoms. If authorised, the treatment will be sold as Paxlovid.
"It's a stunning outcome," Pfizer's chief scientific officer Mikael Dolsten said in an interview.
If you deploy this quickly after infection, we are likely to reduce transmission dramatically.
"We're talking about a staggering number of lives saved and hospitalisations prevented. And of course, if you deploy this quickly after infection, we are likely to reduce transmission dramatically," Mr Dolsten said.
Pfizer also released early data from a second study suggesting the treatment reduced hospitalisations by around 70 per cent in a smaller trial of standard-risk adults, including some higher-risk vaccinated people.
Pfizer said those results showed a positive trend, but were not statistically significant. They are following the results and plan to release data from the final 20 per cent of participants in the 1,100-patient trial.
The trial did not show that the drug alleviated symptoms of Covid-19 in that population.
Mr Dolsten said he expects authorisation for use in high-risk individuals from the US Food and Drug Administration and other regulatory agencies soon. He does not believe an FDA advisory panel meeting will be needed.
"We're in very advanced regulatory dialogues with both Europe and the UK, and we have dialogues with most of the major regulatory agencies globally," Mr Dolsten added.
Pfizer submitted data to the FDA last month, asking for emergency use authorisation of the drug.
The company has said it can have 180,000 treatment courses ready to ship this year and plans to produce at least 80 million more in 2022.
Mr Dolsten said Pfizer is looking to expand that output further as new variants, like the newly-discovered Omicron, could push the need for anti-virals substantially higher. Current vaccines appear to be less effective at preventing infection with Omicron.
