Pfizer’s experimental antiviral pill to treat Covid-19 cuts the risk of hospitalisation or death by 89% when given within three days after the symptoms appear, the pharmaceutical company announced on Friday. The drug is designed to block an enzyme that the coronavirus needs to replicate.

In a statement, Pfizer said that an independent board of experts monitoring its late-stage clinical trial recommended that the study should be stopped because of the drug’s “overwhelming efficacy”.

The company said it will submit the data for the pill, which will be sold under the brand name paxlovid, to the United States Food and Drug Administration as soon as possible.

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The results suggest that Pfizer’s drug is more effective than the antiviral pill developed by pharmaceutical company Merck. Last month, the drug maker had said that its pill, molnupiravir, cut the risk of hospitalisation or death by approximately 50% when given to those vulnerable early in their infections.

Merck is awaiting federal authorisation in the United States. On Thursday, the United Kingdom approved molnupiravir, becoming the first country in the world to approve a pill to treat mild to moderate Covid-19.

However, full trial data is not yet available from either company.

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On Friday, Pfizer said the company has been testing the antiviral pill in adults with Covid-19, who are considered at increased risk of developing severe illness. “Each patient was randomized (1:1) to receive paxlovid or placebo orally every 12 hours for five days,” the company said in the statement.

Pfizer’s chief executive Albert Bourla said the results were “a real game-changer in the global efforts to halt the devastation of this pandemic”.

He added: “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 hospitalisations.”