London: Britain's health regulators on Thursday approved the world's first pill to treat cases of symptomatic COVID-19, dubbed a "gamechanger" for those most vulnerable to the deadly coronavirus.

The Medicines and Healthcare products Regulatory Agency (MHRA) said the antiviral Lagevrio (molnupiravir) was found to be safe and effective at reducing the risk of hospitalisation and death in people with mild to moderate COVID-19, who are at increased risk of developing severe disease.

Molnupiravir, originally created to treat flu, could go on to be prescribed twice a day to vulnerable patients recently diagnosed with COVID-19 after it proved effective in clinical trials.

"Today is a historic day for our country, as the UK is now the first country in the world to approve an antiviral that can be taken at home for COVID-19. This will be a gamechanger for the most vulnerable and the immunosuppressed, who will soon be able to receive the ground-breaking treatment, said UK Health Secretary Sajid Javid.

"We are working at pace across the government and with the NHS to set out plans to deploy molnupiravir to patients through a national study as soon as possible. This antiviral will be an excellent addition to our armoury against COVID-19, and it remains vital everyone comes forward for their life-saving COVID-19 vaccine particularly those eligible for a booster to ensure as many people as possible are protected over the coming months, he said.

Molnupiravir has been authorised for use in people who have mild to moderate COVID-19 and at least one risk factor for developing severe illness. Such risk factors include obesity, old age over 60, diabetes mellitus, or heart disease.

Developed as a tablet by Ridgeback Biotherapeutics and Merck Sharp & Dohme (MSD), Lagevrio works by interfering with the virus' replication. This prevents it from multiplying, keeping virus levels low in the body and therefore reducing the severity of the disease.

Based on the clinical trial data, Lagevrio is most effective when taken during the early stages of infection and so the MHRA recommends its use as soon as possible following a positive COVID-19 test and within five days of symptoms onset.

"Following a rigorous review of the data by our expert scientists and clinicians, we are satisfied that Lagevrio (molnupiravir) is safe and effective for those at risk of developing severe COVID-19 disease and have granted its approval, said Dr June Raine, MHRA Chief Executive.

"Lagevrio is another therapeutic to add to our armoury against COVID-19. It is also the world's first approved antiviral for this disease that can be taken by mouth rather than administered intravenously. This is important, because it means it can be administered outside of a hospital setting, before COVID-19 has progressed to a severe stage, she said.

The health authorities stressed that the new pill is not intended to be used as a substitute for vaccination against COVID-19.

Professor Sir Munir Pirmohamed, Chair of the Commission on Human Medicines, said: "In clinical trials, Lagevrio was found to be effective in reducing the risk of hospitalisation or death for at-risk non-hospitalised adults with mild to moderate COVID-19 by 50 per cent.

"Based on this and other data that has been carefully reviewed by the Commission and its expert group, it is clear Lagevrio is another safe and effective treatment to help us in our fight against COVID-19.

The new tablet targets an enzyme that the virus uses to make copies of itself, introducing errors into its genetic code. That should prevent it from multiplying and keeping virus levels low in the body as well as reducing the severity of the disease. The approach should make the treatment equally effective against new variants of the virus as it evolves in the future.