Pfizer says early trial results show its new COVID-19 pill reduced the risk of hospitalisation or death by up to 89%.
The company has claimed its new drug showed “overwhelming efficacy” against severe illness.
Pfizer says the antiviral medicine - named PAXLOVID - is designed to be administered orally, so it can be prescribed quickly “at the first sign of infection or at first awareness of an exposure”.
In preliminary results from a study of the drug's effectiveness, no deaths were reported in patients who received the medication - compared to 10 deaths among those who received a placebo.
Trials have now been halted while Pfizer seeks approval for the wider use of the drug.
Albert Bourla, Pfizer Chairman and Chief Executive Officer, said: “Today’s news is a real game-changer in the global efforts to halt the devastation of this pandemic.
“These data suggest that our oral antiviral candidate, if approved or authorized by regulatory authorities, has the potential to save patients’ lives, reduce the severity of COVID-19 infections, and eliminate up to nine out of ten hospitalizations.”
The drug has not yet been approved for wider use in the US, with Pfizer now saying it will submit data to regulators as soon as possible.
Pfizer's announcement comes on the same week the UK became the first country to approve another antiviral medication - Merck's molnupiravir - for use.
Full trial results have not yet been released by either Pfizer or Merck.
Merck's drug was shown last month to halve the likelihood of dying or needing hospital treatment for COVID-19.
However, experts have cautioned against comparing the pills at this stage due to differences in approaches to the studies.
Speaking on Newstalk Breakfast today, Tánaiste Leo Varadkar said it will be important for Ireland to authorities such pills as part of the continuing response to the pandemic.