The U.K. is struggling to stock up on supplies of a potentially game-changing coronavirus vaccine, a top government official has said.

Kate Bingham, chair of the U.K. Vaccine Taskforce, said only 4 million doses of the Oxford-AstraZeneca shot will be available by the end of the year, far fewer than the 30 million that were due to be ready by September. AstraZeneca declined to comment.

The question is moot for now given that no vaccine has been approved for use and trials are still ongoing. But the difficulties cast doubt on how fast the U.K. will be able to deploy a vaccine that officials see as potentially critical in allowing life to return to normal.

Boris Johnson’s government has been accused in the past of promising more than it is able to deliver and the news that its vaccine planning is behind schedule risks fueling further criticism of his handling of the pandemic.

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Despite the supply limitations, health officials in England said doctors across the country are being put on stand by to administer vaccines just in case shots are approved for use before the end of this year.

The U.K.’s drug regulator has started accelerated reviews of vaccines under development by Pfizer Inc. and AstraZeneca Plc, as Britain gets ready to approve the first successful shot as quickly as possible.

Speaking to a Parliament’s science committee, Bingham estimated the U.K. would have 4 million doses of the Oxford vaccine available to deploy by the end of the year, and as many as 10 million doses of the Pfizer-BioNTech vaccine.

“We’re going to have more vaccine than we’ll be able to deploy is my expectation,” Bingham said. “I don’t think vaccine supply is going to be the limiting step.”

She said the odds of having a vaccine at some point in the next year that could wipe out the virus are probably “very slim.” The possibility of having a vaccine during that period that reduces illness and deaths is “very high,” she predicted. “The data being generated so far by multiple vaccines and companies is pretty good,” she said.