The first dose of the Oxford-AstraZeneca coronavirus vaccine has been given in the UK.
Dialysis patient Brian Pinker, 82, became the first person to receive the jab.
The government has ordered 100 million doses of the vaccine, following the roll-out of the Pfizer vaccine, which was the first to be approved.
What is the Oxford vaccine and how does it work?
It is made from a weakened version of a common cold virus (known as an adenovirus) from chimpanzees. It has been modified to look more like coronavirus - although it can't cause illness.
When the vaccine is injected into a patient, it prompts the immune system to start making antibodies and primes it to attack any coronavirus infection.
Research has shown it is highly effective.
Unlike Pfizer's jab - which has to be kept at an extremely cold temperature (-70C) - the Oxford vaccine can be stored in a normal fridge. This makes it much easier to distribute.
How has the vaccine been produced so quickly?
Oxford University researchers had already done a lot of work before 2020 on developing a vaccine which could be adapted to tackle different diseases.
That meant a lot of the building blocks were already in place, and scientists weren't starting from scratch.
The vaccine has been through all the usual research stages, although for speed these have overlapped when they would usually happen one after another.
And the UK's medicines regulator - the MHRA - carried out a "rolling review" of data all last year.
When was it approved?
The vaccine was approved for use by the MHRA on 30 December and the first doses were given five days later.
To start with, six hospital trusts - in Oxford, London, Sussex, Lancashire and Warwickshire - are administering the vaccine, with 530,000 doses ready for use.
Most other available doses will be sent to hundreds of GP-led services and care homes across the UK later in the week, according to the Department of Health and Social Care (DHSC).
How effective is the Oxford vaccine?
The Oxford-AstraZeneca vaccine has been shown to be safe and to provoke an immune response in people of all ages, including the over-55s.
Trial participants were given different dosing regimens - some received two full doses and some half a dose followed by a full dose.
The MHRA approved the use of two full doses, which was found to be 62% effective.
And as with the other vaccines, scientists don't yet know if it stops people catching Covid - that's something they won't know until they can see the impact of vaccination over time.
Is the Oxford vaccine as good as the Pfizer?
Trials showed the Pfizer vaccine was 95% effective, but there were differences in the way the trials were carried out, so directly comparing the two results is difficult.
And it's important to remember that even the lower 62% figure is a better result than the best flu jab, which is about 50% effective.
What is more, no-one who received the Oxford vaccine was hospitalised or became seriously ill due to Covid.
How long does it protect against Covid for?
As with all the vaccines being developed against coronavirus, we don't know yet.
It may be that people need annual vaccinations, as happens with the flu jab.
Which vaccine will I get?
You will not be given a choice about which vaccine you get.
Recommendations on which groups get the vaccine are made by the JCVI - the Joint Committee on Vaccination and Immunology - an independent group of scientists.
There are nine priority groups, amounting to more than 25 million people.
The over 80s, care home residents and front-line health and care staff are being offered the jabs first.
It will then be rolled out to other groups including all the over 50s and younger adults with health conditions.