The British government has ordered 40 million further doses of Valneva's Covid-19 vaccine candidate for 2022, bringing its total orders to 100 million, the French drugmaker said on Monday.
Britain could still order a further 90 million doses between 2023 and 2025, the company said.
The firm, which expects a read-out of its Phase I/II clinical trial within three months, said it had already started commercial production in Scotland.
The Scottish site is ready to supply the vaccine as soon as it is proven to be safe, and effective and has been approved by the British healthcare watchdog, the interim chair of government's vaccines taskforce, Clive Dix, said in a statement.
"The further 40 million doses secured through today's deal significantly bolsters our portfolio and gives us future flexibility should we need to revaccinate any of the UK population," Dix added.
Britain's trade minister said on Sunday she was confident the country's vaccination programme was secure following a row with the European Union about vaccine supplies after receiving guarantees from Brussels.
Valneva hopes its Covid-19 vaccine can start to be used in Britain between July and September, its chief executive was quoted as saying in January.