An antiviral drug originally developed to treat influenza has been shown to reduce hospitalisation and death from Covid-19 by as much as 50 per cent in patients recently infected with the virus, early trial results suggest.

It is now hoped the drug, administered in oral form, will be play a key role in treating people who test positive for Covid-19 and prevent their infection from culminating in severe disease.

Molnupiravir (development codes MK-4482 or EIDD-2801) was developed at Emory University before being acquired by Ridgeback Biotherapeutics, who later partnered with Merck & Co. to develop and commercialise the molecule further.

It is thought molnupiravir works by interfering with an enzyme that the virus needs to replicate, thereby preventing it from further spreading throughout the body.

If authorised for use as planeed, molnupiravir will be the first oral antiviral medication for Covid-19. There are currently two approved ways of treating the disease: using steroids, such as dexamethasone, or by administering monocloncal antibodies intravenously.

Preliminary data from Merck’s trial is based on around 800 adult patients with mild to moderate Covid-19 judged to be at greater risk of serious disease owing to underlying comorbidities such as obesity, diabetes or heart disease.

Among the half of patients taking molnupiravir twice a day, 7.3 per cent were admitted to hospital over the course of 30 days. This compared with 14.1 per cent of the second group of patients who were given a placebo.

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The drug also appeared to lower the risk of mortality by 50 percent, though the numbers are small and experts have cautioned against over-interpreting the data. There were no deaths among the molnupiravir group, while eight of those who received the placebo died from Covid-19.

Upon reviewing the data, the US FDA recommended stopping the phase three trial early to begin the process of applying for emergency authorisation.

A course of molnupiravir is expected to cost around £500 or $650. An official at Merck said the company will only be able to make 10 million doses before the end of the year, 1.7 million of which are reserved for the US.