Up to 267 million doses of COVID vaccines were purchased by the government at a cost of £2.9 billion, according to the public spending watchdog.
And the National Audit Office (NAO) estimates the total cost of buying and deploying vaccines - and investing in global access schemes - could reach £11.7bn.
Any booster doses needed in future would be on top of that.
It's the first time that an authoritative figure has been put on the cost of the vaccine roll-out.
The government signed deals with five companies to supply vaccines, with four of them agreeing to priority access.
Non-binding agreements for another 90 million doses were also made with two others, including GSK/Sanofi - which last week announced its vaccine would be delayed because it had failed to work as well as had been hoped.
The outlay includes £914m in upfront payments for manufacturing and clinical trials.
Only one company agreed to fully refund money if its vaccine failed to win approval from the regulatory authorities.
Another two agreed to a partial refund, with the final two refusing to hand back any money.
Taxpayers may incur additional costs because four of the five companies with signed contracts demanded immunity from legal action and claims for damages, with no cap on the liability to government.
Meg Hillier MP, Chair of the Committee of Public Accounts, praised scientists and the medicines regulator for developing and approving vaccines so quickly.
"It was clearly right to back a number of horses - nobody could have known which vaccines would work, or when they might be approved.
"But the accountability arrangements were highly unusual - even though huge sums of money are involved.
The NAO report also reveals the extraordinary scale of the vaccine roll-out.
NHS England and NHS Improvement calculate that if three quarters of the adult population had two doses of vaccine it would need a total of 46,000 NHS staff, with 26,000 of them administering the injection.
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Gareth Davies, the head of the NAO, said: "Developing and securing an effective vaccine is central to reducing the impact of COVID-19 on society and saving lives."
He added: "Government has worked quickly and effectively to secure access to potential vaccines, using the available information to make big decisions in an inherently uncertain (time)."
