The UK has approved a Covid-19 antiviral pill jointly developed by US-based Merck & Co Inc and Ridgeback Biotherapeutics to become the first country in the world to recommend the drug, molnupiravir.

The nod is the first for an oral antiviral treatment for Covid-19 and the first for a coronavirus disease drug that will be administered widely in the community.

“We are now working across government and the NHS to urgently get this treatment to patients initially through a national study so we can collect more data on how antivirals work in a mostly vaccinated population,” UK vaccines minister Maggie Throup told parliament.

The Medicines and Healthcare products Regulatory Agency (MHRA) recommended molnupiravir for use in people with mild to moderate Covid-19 and at least one risk factor for developing severe illness, such as obesity, older age diabetes, and heart disease.

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The agency said, citing clinical data, that it will be administered as soon as possible following a positive Covid-19 test and within five days of the onset of symptoms of the viral disease. It is to be taken twice a day for five days.

Professor Stephen Powis, national medical director for the National Health Service (NHS) in England, said the drug would be administered to patients at higher risk of complications. Powis added that a wider rollout will follow if it is clinically and cost-effective in reducing hospitalisations and death.

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The antiviral pill, which will be branded as Lagevrio in Britain, targets an enzyme the coronavirus, which causes Covid-19, uses to reproduce itself, inserting errors into its genetic code that slow its ability to spread and take over human cells. That genetic activity has led some independent experts to question whether the drug could potentially cause mutations leading to birth defects or tumours.

Merck has said that viral sequencing done so far has shown molnupiravir is effective against all variants of the coronavirus, including the more-infectious Delta, which is responsible for the worldwide surge in hospitalisations and deaths recently. The company has not disclosed details on molnupiravir’s side effects but said that rates of those problems were similar between people who got the drug and those who received dummy pills.

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Merck announced preliminary results in September showing its drug cut hospitalisations and deaths by half among patients with early Covid-19 symptoms. However, the results haven’t yet been peer reviewed or published in a scientific journal.

US advisers will meet on November 30 to review the drug’s safety and efficacy data and vote on whether molnupiravir should be authorised.

Pfizer and Roche are also racing to develop easy-to-administer antiviral pills for Covid-19.