The Moderna Covid-19 vaccine is the third jab to be rolled out in the UK, behind Pfizer in December and Oxford/AstraZeneca in January.
Here's everything you need to know about the Moderna vaccine.
How effective is it against coronavirus?
Phase three study results suggested vaccine efficacy against the disease was 94.1% with the Moderna jab, against severe Covid-19 this was more positive still at 100%.
More than 30,000 people in the US took part in the trial, from a wide range of age groups and ethnic backgrounds.
Two doses were given 28 days apart so researchers could evaluate safety and any reaction to the vaccine.
The analysis was based on 196 cases, of which 185 cases of Covid-19 were observed in the placebo group versus 11 cases observed in the active vaccine group.
Moderna also released data relating to severe cases.
All 30 severe cases occurred in the placebo group and none in the group which had received the vaccine, known as mRNA-1273.
How many doses of Moderna does the UK have?
The government has bought 17 million doses - enough to vaccinate about 8.5 million people.
How does the vaccine work?
The Moderna jab is a messenger RNA (mRNA) vaccine.
Conventional vaccines are produced using weakened forms of the virus, but mRNAs use only the virus's genetic code.
An mRNA vaccine is injected into the body, where it enters cells and tells them to create antigens.
These antigens are recognised by the immune system and prepare it to fight the virus. No actual virus is needed to create an mRNA vaccine.
This means the rate at which the vaccine can be produced is accelerated.
Is the vaccine safe?
Like all the vaccines, the jab has been tested extensively and approved by the British regulator for use using the highest safety measures.
Moderna said the vaccine was generally well tolerated, with no serious safety concerns identified.
Some people may experience pain around the injection-site after their first jab.
While symptoms after the second dose could include fatigue, muscle pain, joint pain, headache, other pain and redness at the injection site.
For those who did experience any of these, they were all generally short-lived.
Is the Moderna vaccine effective against variants?
In late January, the company behind the vaccine said it was effective against both the strain first detected in Kent and the mutation which first emerged in South Africa.
Moderna said laboratory tests found no significant impact on antibodies against the UK variant relative to prior variants.
While there was a six-fold reduction in neutralising antibodies produced against the South African variant, the levels remained above those that are expected to be protective, Moderna said.
What stage is the Moderna rollout at in each of the four UK nations?
People in Wales will get first doses of the vaccine from Wednesday, at the West Wales General Hospital in Carmarthen.
The rollout will begin in England "as soon as possible this month," a Department of Health and Social Care spokesperson said.
Scotland’s First Minister Nicola Sturgeon said the first batch of Moderna vaccines had arrived in the country on Monday and will be delivered over the coming months.
It has not been confirmed when the rollout of Moderna will begin in Northern Ireland.
Coronavirus - What you need to know