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.
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.