The UK government will confirm later whether it will join the EU vaccine scheme, Number 10 says, amid reports it will opt out.
A spokesman said the scheme “would have to work for the UK” and decisions were taken “in the national interest”.
It comes after the Telegraph reported ministers rejected the chance to join over concerns the UK would not get the number of vaccines it needs on time.
The EU scheme aims to secure supplies of potential coronavirus vaccines.
The EU Commission plans to enter into agreements with individual vaccine producers on behalf of the bloc’s member states as part of the multi-million pound programme.
In return for the right to buy a specified number of vaccine doses in an agreed timeframe and price, the Commission will finance a part of the vaccine producer’s upfront costs.
Reacting to reports the UK will opt out of the initiative, the Wellcome Trust said countries “urgently” needed to work together “if we’re to stand any chance of delivering global equitable access to a Covid-19 vaccine”.
The Telegraph reported that the government believed limits on the number of doses allocated to member states could result in the UK not getting the vaccines it needs.
A source told the paper: “The terms just weren’t right for us. The EU scheme wouldn’t allow the UK to do anything more than it currently is.”
The newspaper reported that officials believed that signing up to the scheme could delay the rollout of a vaccine in the UK by up to six months as talks on distribution took place.
But Alex Harris, head of global policy at the Wellcome Trust, said: “The EU vaccine initiative’s cap on how many doses participating countries get is the best way to ensure there is enough vaccine for those in need in the rest of the world.
“Delivering vaccine according to need and not who can pay the highest price, is not just morally right, but also the fastest way to end this pandemic.
“We urge the UK government to follow the EU’s lead and only secure vaccine doses for those who need it most (healthcare workers, over 65s and other vulnerable groups).”
He said this approach was “critical” for the first “six to nine months of early vaccine availability” as global manufacturing capacity was “unlikely to match demand”.
In the UK, human trials of a vaccine are under way in London and Oxford.
Worldwide, about 200 groups are working on vaccines and 18 are now being tested on people in clinical trials.
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Reacting to reports the UK was not going to join the EU scheme, Lib Dem leadership hopeful Layla Moran tweeted: “Walking away from the EU vaccines scheme is putting ideology ahead of public health.”
And Labour MP Bell Ribeiro-Addy tweeted: “By refusing to join the EU’s vaccine scheme, the government is yet again putting ideology before saving lives.”