Britain's medical regulator on Friday approved Moderna's Covid-19 vaccine for use, the health ministry said, adding that it had agreed to purchase an additional 10 million doses of the shot as it eyed a spring rollout of the shot.
Three Covid-19 vaccines have now been approved for use in Britain, with Pfizer//BioNTech's shot and one developed by Oxford University and AstraZeneca already being rolled out.
The Moderna shot is not expected to play a part in the first stage of Britain's vaccine rollout. Britain now has 17 million doses of Moderna's vaccine on order, and supplies will begin to be delivered to the UK from the spring once Moderna expands its production capability.
"We have already vaccinated nearly 1.5 million people across the UK and Moderna's vaccine will allow us to accelerate our vaccination programme even further once doses become available from the spring," health minister Matt Hancock said.
Britain was the first to approve Pfizer's and AstraZeneca's vaccines as it bids to ramp up its vaccine rollout quickly but is behind some other major countries in giving the go-ahead to the Moderna shot.
Moderna's vaccine was 94% effective in preventing disease in late-stage clinical trials, and it has already been given regulatory approval for use in the United States, Canada, the European Union and Israel.
Britain is attempting to vaccinate the elderly, the vulnerable and frontline workers - around 15 million people - by mid-February, to ease a new strict lockdown imposed after a spike in cases to daily records.
Although Moderna's vaccine will not help meet that target, it will help ease supply constraints that Hancock has cited as being a limiting factor in the rollout.
"This is excellent news and a further crumb of comfort amid the huge levels of Covid-19 currently circulating around the UK," said Michael Head, Senior Research Fellow in Global Health at the University of Southampton.
"When these Moderna vaccines arrive, they will help to ease any bottlenecks or delays in the administration programme."