Britain on Friday approved the use of a fourth Covid vaccine, hoping to boost a countrywide inoculation drive to allow its economy to reopen fully despite concerns about a new variant.
The Medicines and Healthcare products Regulatory Agency (MHRA) approved the single-shot Johnson & Johnson jab, after previously backing the Pfizer, AstraZeneca and Moderna shots.
Prime Minister Boris Johnson called it "very welcome news and another boost to our hugely successful vaccination programme".
"As we encourage everyone to get their jabs, the single-dose… vaccine will play an important role in helping us protect people from the virus," he wrote on Twitter.
"When you get the call, get the jab."
Health Secretary Matt Hancock said the mass vaccination campaign — the biggest in Britain's history — had already saved more than 13,000 lives.
The latest regulatory green light "means that we now have four safe and effective vaccines approved to help protect people from this awful virus", he added.
Britain has ordered 20 million doses of the vaccine, which was found to be 72 percent effective in preventing moderate to severe coronavirus infection, according to a US trial.
The European Medicines Agency said in April that a warning about unusual blood clots with low blood platelet count should be added to the J&J product information following cases in the United States.
Britain has administered more than 62 million shots so far, mainly using the Pfizer and AstraZeneca vaccines.
The J&J vaccine comes on stream as younger people are called for their jab, amid concern over the rise of the so-called Indian variant.
After months of falling cases, infections have started to rise again due to the emergence of the variant, which has put in doubt plans for a full reopening of the country on June 21.
Business Secretary Kwasi Kwarteng said Friday, however, "it was impossible for anyone to know what the situation will be like in a week or two weeks' time".
"We'll be looking at the data, we've said repeatedly that we won't make a final decision about the 21st of June until the 14th of June," he told Sky News.