Britain could begin vaccinating priority groups, such as health and social care workers, if the treatment proves successful.
Britain has signed a deal for the supply of up to 60 million doses of a potential coronavirus vaccine developed by Sanofi and GlaxoSmithKline (GSK).
Human clinical studies of the vaccine will begin in September followed by a phase 3 study in December.
The government has now signed deals for four different types of potential coronavirus vaccines and a total of 250 million doses.
If the Sanofi/GSK treatment proves successful, the UK could begin vaccinating priority groups such as frontline health and social care workers and those at increased risk from coronavirus.
The vaccinations would take place as early as the first half of next year, the Department for Business, Energy & Industrial Strategy (BEIS) said.
Financial terms of the agreement between the government and Sanofi/GSK were not disclosed.
No vaccine has yet been approved to treat or prevent COVID-19.
Business Secretary Alok Sharma said: “Our scientists and researchers are racing to find a safe and effective vaccine at a speed and scale never seen before.
“While this progress is truly remarkable, the fact remains that there are no guarantees.
“In the meantime, it is important that we secure early access to a diverse range of promising vaccine candidates, like GSK and Sanofi, to increase our chances of finding one that works so we can protect the public and save lives.”
Sanofi and GSK, which first teamed up in April, have confirmed that regulatory approval for their vaccine could be won by the first half of 2021 if clinical data was positive.
Hugo Fry, the UK managing director of Sanofi, was asked how the vaccine would be delivered to patients if it works.
He told Sky News: “Bodies like Public Health England are really looking at – ‘right, that volume of vaccines, how can we get it?’
Asked when the vaccine might be available to patients if it works, Mr Fry added: “If everything goes to plan, we’re looking at this time next year. July, August time 2021, for this particular vaccine.”
The UK deal comes as the EU Commission has signed an agreement with Gilead to secure access to the COVID-19 drug Remdesivir.
Britain has moved early in striking vaccine supply deals, and ministers have stressed the importance of securing supplies of a range of candidates.
The UK struck deals for 30 million doses of the experimental BioNTech/Pfizer vaccine last week, and agreed a deal in principle for 60 million doses of the Valneva vaccine.
That followed a previously announced pact with AstraZeneca for production of 100 million doses of its potential vaccine, being developed in partnership with Oxford University.
Britain now has a total of 250 million doses of potential coronavirus vaccines available.
The vaccine produced by GSK and Sanofi, which together have the largest vaccine manufacturing capability in the world, is based on the existing DNA-based technology used to produce Sanofi’s seasonal flu vaccine.
Kate Bingham, chairwoman of the Government’s Vaccines Taskforce, said: “This diversity of vaccine types is important because we do not yet know which, if any, of the different types of vaccine will prove to generate a safe and protective response to COVID-19.
“Whilst this agreement is very good news, we mustn’t be complacent or over-optimistic.
“The fact remains we may never get a vaccine and, if we do get one, we have to be prepared that it may not be a vaccine which prevents getting the virus, but rather one that reduces symptoms.”
The government said almost 72,000 people have volunteered in the past week to receive information about joining clinical studies to find a vaccine but many more are needed.
Ministers hope to get 500,000 people signed up by October.
Roger Connor, president of GSK Vaccines, said: “We believe that this adjuvanted vaccine candidate has the potential to play a significant role in overcoming the COVID-19 pandemic, both in the UK and around the world.
“We thank the UK government for confirmation of purchasing intent, which supports the significant investment we are already making as a company to scale up development and production of this vaccine.”
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