Britain's Medicines and Healthcare products Regulatory Agency (MHRA) granted emergency use approval to the Pfizer-BioNTech vaccine, which they say is 95% effective in preventing illness, just 23 days since Pfizer published the first data from its final stage clinical trial.
"Fantastic news," Johnson told parliament, though he cautioned that people should not get too carried away.
"At this stage it is very, very important that people do not get their hopes up too soon about the speed with which we will be able to roll out this vaccine."
The world's big powers have been racing for a vaccine for months to begin the long road to recovery, and getting there first may be seen as a coup for Johnson's government, which has faced criticism over its handling of the crisis.
The approval of a shot for use close to a year since the novel coronavirus emerged in Wuhan, China, is a triumph for science, Pfizer boss Albert Bourla and his German biotechnology partner BioNTech .
Both the United States and the European Union's regulator are sifting through the same Pfizer vaccine trial data, but have not yet given their approval.
Britain's breakneck speed drew criticism from Brussels where, in an unusually blunt statement, the EU's drugs regulator said its longer procedure was more appropriate as it was based on more evidence and required more checks.
British leaders said that, while they would love to get a shot themselves, priority had to be given to those most in need - the elderly, those in care homes and health workers.
Amid the celebratory rhetoric, Germany's ambassador to Britain Andreas Michaelis publicly scolded a British minister for presenting it as a national triumph.
"I really don't think this is a national story. In spite of the German company BioNTech having made a crucial contribution, this is European and transatlantic," Michaelis said.
'NO CORNERS CUT'
The U.S. drugmaker said Britain's emergency use authorization marked a historic moment in the fight against COVID-19. Pfizer announced its vaccine breakthrough on Nov. 9 with stage III clinical trial results.
"This authorization is a goal we have been working toward since we first declared that science will win, and we applaud the MHRA for their ability to conduct a careful assessment and take timely action to help protect the people of the UK," said CEO Bourla.
Britain's medicines regulator approved the vaccine in record time by doing a "rolling" concurrent analysis of data and the manufacturing process while Pfizer raced to conclude trials.
"No corners have been cut," MHRA chief June Raine said in a televised briefing from Downing Street, adding that the first data on the vaccine had been received in June and undergone a rigorous analysis to international standards. "Safety is our watchword."
"With 450 people dying of COVID-19 infection every day in the UK, the benefits of rapid vaccine approval outweigh the potential risks," said Andrew Hill, senior visiting research fellow in the Department of Pharmacology at the University of Liverpool.
The U.S. Food and Drug Administration (FDA) will make a decision on emergency use authorization on the Pfizer/BioNTech vaccine in days or weeks after a panel of outside advisors meets on Dec. 10 to discuss whether to recommend it. The FDA often but not always follows the panel's advice.
The European Medicines Agency (EMA) said it could give emergency approval for the shot by Dec. 29.
"The data submitted to regulatory agencies around the world are the result of a scientifically rigorous and highly ethical research and development programme," said Ugur Sahin, chief executive and co-founder of BioNTech .
BioNTech said it expected FDA and EMA to make a decision in mid-December.
Anti-poverty campaigners, meanwhile, warned against rich countries hoarding vaccines at the expense of poorer ones. "The worst thing we can do at this moment is allow a small number of countries to monopolise access to vaccines like this," said Romilly Greenhill, UK director of the ONE organisation.
FIRST IN LINE
Britain said it would start vaccinating those most at risk of dying early next week after it gets 800,000 doses from Pfizer's manufacturing centre in Belgium.
"I strongly urge people to take up the vaccine but it is no part of our culture or our ambition in this country to make vaccines mandatory," Johnson said.
The speed of the rollout depends on how fast Pfizer can manufacture and deliver the vaccine - and the extreme temperature of -70C (-94F) at which the vaccine must be stored.
Britain has ordered 40 million doses of the Pfizer vaccine - enough for just under a third of the population as two shots are needed per person to gain immunity.
Health Secretary Matt Hancock said hospitals were ready to receive the shots and vaccination centres would be set up across the country, but he admitted distribution would be a challenge given storage at temperature typical of an Antarctic winter.
Pfizer has said the shots can be kept in thermal shipping boxes for up to 30 days. Afterwards, the vaccine can be kept at fridge temperatures for up to five days.
Other frontrunners in the vaccine race include U.S. biotech firm Moderna, which has said its shot was 94% successful in late-stage clinical trials, and AstraZeneca AZN.L , which said last month its COVID-19 shot was 70% effective in pivotal trials and could be up to 90% effective.
(Reporting by Guy Faulconbridge and Paul Sandle; Additional reporting by Kate Kelland, Alistair Smout and Estelle Shirgon; Editing by Kate Holton, Carmel Crimmins, Alex Richardson and Nick Macfie) ((firstname.lastname@example.org; 07825218698;))