Britain has said it needed to recruit 6,000 more people onto a trial of Merck's Covid-19 antiviral pill molnupiravir to inform how the drug can be rolled out more widely.

Britain's MHRA medicine regulator approved the pill, made by Merck and Ridgeback Therapeutics, in November, and the government launched a national study to establish the best way to use the drug.

The health ministry said that while 4,500 trial participants had signed up, thousands more were needed to gather the data needed, according to a Reuters report.

The study, called Panoramic, was launched to assess how the antiviral should be used in a largely vaccinated population, given it was assessed in clinical trials on unvaccinated people.