The UK will begin to distribute the Moderna vaccine on Wednesday, strengthening its Covid-19 immunisation programme after concerns over AstraZeneca’s shot and a shortfall of doses this month.
Health Secretary Matt Hancock said the Moderna shot would first be offered in west Wales.
It is the third approved vaccine to be offered in Britain, alongside those from AstraZeneca and partners Pfizer and BioNTech, and its introduction is about two weeks earlier than expected.
The UK ordered 17 million doses of Moderna’s two-shot vaccine.
The success of the vaccine programme is crucial to Prime Minister Boris Johnson’s ambition to fully reopen the UK economy on June 21.
On Tuesday, Mr Johnson sought to reassure people over the AstraZeneca vaccine amid concerns in Europe over possible side effects.
It later emerged that inoculations of children in a study of the vaccine developed by AstraZeneca and the University of Oxford were paused while the UK's drug regulator investigates rare cases of blood clots in adults.
No safety issues arose in the children's trial, the University of Oxford said.
“The UK government has secured vaccines on behalf of the entire nation and the vaccination programme has shown our country working together at its best,” Mr Hancock said.
“Wherever you live, when you get the call, get the jab."
The government said it is on track to meet its target to vaccinate all adults by the end of July, despite a reduction in doses this April and a slower pace than expected in the months ahead.
Vaccination centres and pharmacies are facing a “significant reduction” in supply during April, NHS England said last month, meaning that older people waiting for second doses will be given priority over younger people getting their first shot.
The pace of vaccinations across England is now estimated by the Cabinet Office at an average of 2.7 million a week until the end of July.
That is “considerably slower” than a previous forecast of 3.2 million a week, according to a modelling paper from scientists on a government advisory committee, published on Monday.
Mr Johnson’s spokesman, Jamie Davies, said the government “never talked about details around supplies and deliveries”.
“There will be a slight reduction in April but the key thing to remember is that that doesn’t mean that we’re not on track to meet our pledges,” Mr Davies said on Tuesday.
The UK will be able to offer a first dose to all over-50s by April 15, and to all adults by the end of July, he said.
Vaccines Minister Nadhim Zahawi told the BBC on Tuesday that the Moderna vaccine's introduction would occur “around the third week of April”.
Three in five adults in the UK have been vaccinated so far, Mr Hancock said on Twitter.
The most recent government data shows that more than 31.6 million people received a first dose, and 5.5 million have had a second.
On a visit to an AstraZeneca plant in Macclesfield, north-west England, Mr Johnson urged people to listen to the Medicines and Healthcare Products Regulatory Agency, the UK’s drug watchdog.
“Their advice to people is to keep going out there, get your jab, get your second jab,” he said.