Novavax has formally sought regulatory approval of its coronavirus vaccine in Britain.
The US-based firm submitted its final trial data to drug safety watchdogs, in a move that could see another jab added to the UK's roster.
No10 has already bought 60million doses of the jab. But it is not clear how it would be used, if approved.
Novavax expects a 'positive decision' from the Medicines and Healthcare products Regulatory Agency (MHRA).
Its vaccine, officially known as NVX-CoV2373, would be the first protein-based jab approved in the UK, if given the green light.
Novavax's vaccine, officially known as NVX-CoV2373, would be the first protein-based jab approved in the UK, if given the green light
The Government has ordered 60million doses of Novavax, which the MHRA is currently reviewing. Pfizer is the most-ordered jab in the UK, with 135million due to arrive in Britain by next year. Some 100million doses of AstraZeneca have been ordered, along with 60million doses of the jab made by GSK. Meanwhile, the Government has requested 50million CureVac vaccines, 20million Janssen and 17million Moderna injections. But only four jabs have been approved in the UK: AstraZeneca, Pfizer, Moderna and Janssen
Other injections already approved are either viral vector vaccines that are made from a common cold virus (AstraZeneca and Janssen), or an mRNA vaccine made from enzymes (Pfizer and Moderna).
EVERYTHING YOU NEED TO KNOW ABOUT THE NOVAVAX COVID-19 VACCINE THAT PREVENTED MORE THAN 90% OF PEOPLE FALLING ILL
How does the vaccine work?
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.
Are there advantages of the Novavax vaccine?
Yes. 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.
How effective is the vaccine?
According to results of phase III trials, the jab offers 100 percent protection against severe disease, including all hospital admission and death.
It is 86 percent effective against the Alpha (Kent) variant and 100 percent effective in preventing cases caused by the original strain of the coronavirus.
Has the Novavax vaccine been approved?
Not yet. The UK's Medicines and Healthcare Products Regulatory Agency is reviewing data on the jab.
In the U.S., the data will be examined by regulators at the Food and Drug Administration after Novavax applies for Emergency Use Authorization.
Novavax's contains proteins that mimic the spikes on the coronavirus, causing to produce antibodies to fight the infection. It is administered in two doses 21 days apart.
Protein vaccines already in use include the hepatitis B and meningitis jabs.
Trials showed the vaccine was up to 100 per cent effective at stopping moderate and severe disease.
The UK has ordered more than 400million doses of eight difference vaccines, but only four have been approved by the MHRA: AstraZeneca, Pfizer, Moderna and Janssen.
The agency decides whether to approve any vaccine based on safety, quality and effectiveness data.
Maryland-based Novavax's submission includes data from the phase three clinical trial, which tested the jab on more than 15,000 people in the UK.
It revealed the jab had an efficacy rate of 96.4 against mild, moderate and severe disease caused by the original coronavirus strain.
And it also offered 86.3 percent protection against the Alpha strain.
Meanwhile, a trial of the vaccine on 30,000 people in the US and Mexico found it gave 100 per cent protection against moderate and severe disease.
Trials found the injection to produced a 'robust' antibody response, is safe and only triggered mild side effects.
Stanley Erck, the company's president and chief executive, said: 'This submission brings Novavax significantly closer to delivering millions of doses of the first protein-based Covid vaccine, built on a proven, well-understood vaccine platform that demonstrated high efficacy against multiple strains of the coronavirus.
'We look forward to MHRA's review and will be prepared to deliver vaccine doses following what we anticipate will be a positive decision.
'We thank the clinical trial participants and trial sites in the UK, as well as the UK Vaccines Taskforce, for their support and vital contributions to this programme.'
The MHRA could not provide any details of its review of the jab due to commercial confidentiality.
Novavax said it plans to submit its jab to regulators in Europe, Canada, Australia and New Zealand 'shortly', as well as to the US by the end of the year.
Earlier this month, it was announced that the 15,000 participants in the UK Novavax trial would have to have two further doses of another vaccine to travel abroad.
Thousands of volunteers have been unable to travel because other countries do not recognise Novavax as a valid Covid vaccine.