LONDON, United Kingdom (AFP) — Britain on Thursday lowered the country's virus alert level down one notch from the highest possible, saying a fall in cases had reduced the threat to the state-run National Health Service.

Since January, the country has been at the highest level 5, indicating a "material risk of healthcare services being overwhelmed" and a need for "extremely strict" social distancing.

It is now moving to level 4, indicating a "high or rising level of transmission" with enforced social distancing.

The UK's chief medical officers and the medical director of NHS England said they had agreed to the move as cases have been "consistently declining" and the threat of the NHS "being overwhelmed within 21 days has receded".

Prime Minister Boris Johnson has said he is "very optimistic" that all coronavirus restrictions will be lifted by June 21 as the vaccine roll-out has led to a sharp fall in cases, hospitalisations and deaths.

The UK has administered a first dose of coronavirus vaccine to more than 18 million people.

On Wednesday it reported 9,938 new cases and 442 deaths. Since the start of the pandemic the country has registered more than 4 million cases and over 121,000 people have died.