The COVID-19 vaccine developed by AstraZeneca and Oxford University has been approved for use in the UK, the government has said.
It paves the way for millions more people to be immunised against the virus, with the UK ordering 100 million doses from AstraZeneca, which can vaccinate 50 million people.
The NHS has already vaccinated hundreds of thousands of patients with the Pfizer/BioNTech vaccine and the government said its rollout will continue.
The health service will now start preparing to roll out the Oxford University/AstraZeneca vaccine, with hopes to begin administering the jabs in the new year.
Unlike the Pfizer/BioNTech jab, the newly approved vaccine can be stored at room temperature rather than -70C, which means it will be easier to transport to care homes and doctor's surgeries.
It is also cheap and easy to mass-produce, which will help the UK quickly expand its immunisation campaign.
"The Government has today accepted the recommendation from the Medicines and Healthcare products Regulatory Agency (MHRA) to authorise Oxford University/AstraZeneca’s Covid-19 vaccine for use," Westminster said in a statement.
"This follows rigorous clinical trials and a thorough analysis of the data by experts at the MHRA, which has concluded that the vaccine has met its strict standards of safety, quality and effectiveness."
Health Secretary Matt Hancock added that it was "a moment to celebrate British innovation" as the new vaccine would also be made available at a low cost to the world's poorest regions.
AstraZeneca chief executive Pascal Soriot hailed the "important day" for the millions who would get the jab.
He said: "It has been shown to be effective, well-tolerated, simple to administer and is supplied by AstraZeneca at no profit. We would like to thank our many colleagues at AstraZeneca, Oxford University, the UK government and the tens of thousands of clinical trial participants.
A shift in vaccination strategy
The Joint Committee on Vaccination and Immunisation (JCVI) will also publish its latest advice for the priority groups to receive this vaccine.
It has advised a shift in strategy, with priority to be given to getting as many people as possible in at-risk groups their first dose, rather than providing the required two doses in as short a time as possible.
"Everyone will still receive their second dose and this will be within 12 weeks of their first. The second dose completes the course and is important for longer-term protection," the UK government said.
It added that administering the vaccines in this way will maximise the benefits of both vaccines, according to the JCVI's advice.
"It will ensure that more at-risk people are able to get meaningful protection from a vaccine in the coming weeks and months, reducing deaths and starting to ease pressure on our NHS,"
The announcement came as the UK grappled with a new variant of COVID-19, which saw many European countries shut their borders to the island nation.
The new variant has now been reported in other countries on the continent as well as the US.