The UK has ordered almost 370 million doses of seven coronavirus vaccines in the biggest and most expensive immunisation programme in history.
Two of those vaccines - one by Pfizer/BioNTech and the other by Oxford University/AstraZeneca - have already been injected into the arms of millions of Britons.
A third, developed by Moderna, has been approved by the UK's medicines regulator and is due to be distributed in the spring.
The other four vaccines that have been ordered in the millions were developed by Novavax, Janssen, Valneva and GlaxoSmithKline/Sanofi Pasteur, and are at various stages of ongoing trials.
The National Audit Office said last month that the UK will spend up to £11.7 billion on purchasing, manufacturing and rolling out vaccines.
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More than 7.4 million people in the UK have had a least one dose of a vaccine, as of Thursday
The Novavax jab was just under 90 per cent effective in phase 3 trials in the UK, according to the American firm.
It could be approved by the Medicines and Healthcare products Regulatory Agency within weeks.
The UK was the first country in the world to give emergency use authorisation to the Pfizer/BioNTech jab and the first to use it.
It was also the first to use the Oxford/AstraZeneca vaccine.
Margaret Keenan, 90, was the first person in the UK to be vaccinated against coronavirus.
The grandmother received her first dose of the Pfizer/BioNtech jab at University Hospital in Coventry from nurse May Parsons on December 8, followed by a second dose three weeks later.
Since then, the Government has extended the gap between the first and second dose from three to 12 weeks to vaccinate more people, but the practice has drawn criticism.
All vaccines are required to undergo rigorous testing and have oversight from experienced regulators.
Here is a look at the seven vaccines that the Government has ordered to protect Britons against Covid-19.
Pfizer and BioNTech
Type: mRNA
Doses: 40 million - enough for 20 million people
The vaccine, from the US firm Pfizer and German bioengineering firm BioNTech, is being rolled out across the UK, having been approved for use on December 2 last year.
The first jabs were given six days later.
Analysis from trials shows the vaccine can prevent 95 per cent of people from getting Covid-19, including 94 per cent in older age groups.
Before it was approved for use in the UK, the vaccine was tested on 43,500 people in six countries and no safety concerns were raised.
The Pfizer/BioNTech vaccine is manufactured in Belgium.
It is a messenger RNA (mRNA) vaccine, and doses must be stored at ultra-low temperatures.
Conventional vaccines are produced using weakened forms of the virus, but mRNAs use only the virus’s genetic code.
An mRNA vaccine is injected into the body where it enters cells and tells them to create antigens.
These antigens are recognised by the immune system and prepare it to fight coronavirus.
No actual virus is needed to create an mRNA vaccine. This means the rate at which it can be produced is dramatically accelerated.
As a result, mRNA vaccines have been hailed as potentially offering a rapid solution to new outbreaks of infectious diseases.
Oxford and AstraZeneca
Type: Adenovirus
Doses: 100 million - enough for 50 million people
The jab is being administered throughout the UK, after getting the green light from the Medicines and Healthcare products Regulatory Agency (MHRA) on December 30.
On January 4, dialysis patient Brian Pinker, 82, became the first person in the UK to receive this jab.
Phase 3 trial data showed the jab was 70.4 per cent effective on average across two different dose regimes and possibly up to 90 per cent when one half dose is given followed by a further full dose.
The retired maintenance manager received the jab from nurse Sam Foster at Oxford's Churchill Hospital.
The vaccine – called ChAdOx1 nCoV-19 – uses a harmless, weakened version of a common virus which causes a cold in chimpanzees.
Researchers have already used this technology to produce vaccines against a number of pathogens including flu, Zika and Middle East Respiratory Syndrome (Mers).
The virus is genetically modified so that it is impossible for it to grow in humans.
Scientists have transferred the genetic instructions for coronavirus’s specific “spike protein” – which it needs to invade cells – to the vaccine.
When the vaccine enters cells inside the body, it uses this genetic code to produce the surface spike protein of the coronavirus.
This induces an immune response, priming the immune system to attack coronavirus if it infects the body.
The majority of the Oxford/AstraZeneca vaccine is set to be manufactured in the UK, despite initial doses coming from Germany.
Moderna
Type: mRNA
Doses: 17 million - enough for 8.5 million people
The jab from the US biotech firm has been approved for use in the UK, but doses will not be available until the spring.
It is the third vaccine to receive approval from the UK medicines regulator.
The phase 3 results suggest vaccine efficacy against the disease was 94.1 per cent, and vaccine efficacy against severe Covid-19 was 100 per cent.
More than 30,000 people in the US took part, from a wide range of age groups and ethnic backgrounds.
Two doses were given 28 days apart so researchers could evaluate safety and any reaction to the vaccine.
Moderna said the vaccine was generally well tolerated, with no serious safety concerns identified to date.
Like the Pfizer/BioNTech jab, it is an mRNA vaccine.
It must also be stored at ultra-low temperatures.
Novavax
Type: Protein adjuvant.
Doses: Under the in-principle agreement, the UK has secured 60 million doses of the Novavax vaccine
The UK is providing infrastructure to Novavax in running a phase three clinical trial in the UK, and plans to manufacture its vaccine in the UK with Fujifilm Diosynth Biotechnologies.
Results from those trials show the vaccine offers 89 per cent protection against Covid-19, but it still requires approval from the MHRA, which could take several weeks.
It is the first to show in trials that it is effective against the new and more infectious UK variant of the virus.
More than 15,000 people in the UK took part in the clinical trial, which was supported by the UK National Institute for Health Research.
Some 27 per cent of those in the UK were over the age of 65.
Jabs should be available in the second half of 2021. The vaccine will be produced in Stockton-on-Tees in County Durham.
The Novavax vaccine works like other vaccines by teaching the immune system to make antibodies to the coronavirus spike protein.
Researchers inserted a modified gene into a virus, called a baculovirus, and allowed it to infect insect cells.
Spike proteins from these cells were then assembled into nanoparticles which, while they look like coronavirus, cannot replicate or cause Covid-19.
These nanoparticles are then injected into the body via the vaccine where the immune system mounts an antibody response.
If the body encounters coronavirus in the future, the body is primed to fend it off.
The vaccine is given as two doses.
While the jabs from Pfizer/BioNTech and Moderna need to be kept at ultra-low temperatures, the Novavax jab is stable for up to three months in a normal fridge.
Janssen
Type: Adenovirus
Doses: Some 30 million doses have been secured from Janssen, which is owned by the US company Johnson & Johnson (J&J).
Johnson & Johnson announced on Friday that its single-shot vaccine was 72 per cent effective in preventing Covid-19 in the United States but a lower rate of 66 per cent was observed globally in the large trial conducted across three continents and against multiple variants.
The company plans to seek emergency use authorisation from the US Food and Drug Administration next week.
In the trial of nearly 44,000 volunteers, the level of protection against moderate and severe Covid-19 was 66 per cent in Latin America and just 57 per cent in South Africa, where a particularly worrying variant of the novel coronavirus is circulating.
J&J's main study goal was the prevention of moderate to severe Covid-19, and the vaccine was 85 per cent effective in stopping severe disease and preventing hospitalisation across all geographies and against multiple variants 28 days after immunisation.
That level of prevention "will potentially protect hundreds of millions of people from serious and fatal outcomes of Covid-19," said Dr Paul Stoffels, J&J's chief scientific officer.
Adenoviral vaccines are based on weakened versions of adenoviruses, which are a group of viruses that typically infect membranes of the eyes, respiratory tract, urinary tract, intestines and nervous system, and include the common cold.
Valneva
Type: Inactivated whole virus
Doses: There is an in-principle agreement for 60 million doses.
Valneva is a biotech company based in France.
If the vaccine is proven to be safe, effective and suitable, the UK has secured an option to acquire a further 40 million doses
Valneva's site in Livingston, West Lothian, will manufacture the vaccine. Clinical trials are ongoing.
Inactivated whole virus vaccines contain whole bacteria or viruses which have been killed, or small parts of bacteria or viruses, such as proteins or sugars, which cannot cause disease.
GlaxoSmithKline (GSK) and Sanofi Pasteur
Type: Protein adjuvant
Doses: 60 million
Clinical trials continue for the vaccine from Brentford-based pharmaceutical firm GlaxoSmithKline and Sanofi Pasteur, the vaccines division of the French pharmaceutical company Sanofi.
Interim results of early phases of the trial showed an immune response comparable to patients who recovered from Covid-19 in adults aged 18 to 49 years, but a low immune response in older adults.
In protein adjuvant vaccines,an adjuvant is added to some vaccines to enhance the immune response, and has been shown to create a stronger and longer lasting immunity against infections than the vaccine alone.
The use of an adjuvant may reduce the amount of vaccine protein required per dose, which allows more vaccine doses to be produced.
