Britain has become the first country in the world to approve a potentially game-changing Covid-19 antiviral pill jointly developed by US-based Merck & Co Inc and Ridgeback Biotherapeutics, in a boost to the fight against the pandemic.

Britain's Medicines and Healthcare products Regulatory Agency (MHRA) recommended the drug, 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, Reuters reported.

It will be administered as soon as possible following a positive Covid-19 test and within five days of the onset of symptoms, the regulator said, citing clinical data.

The pill, which will be branded as Lagevrio in Britain, is designed to introduce errors into the genetic code of the coronavirus that causes Covid-19 and is taken twice a day for five days.