Britain on Friday asked its medicine regulator to assess Oxford University and AstraZeneca's COVID-19 vaccine candidate for temporary supply, a step towards beginning a roll-out before the end of the year.

AstraZeneca expects 4 million doses to be available in Britain by the end of next month, and health minister Hancock is targeting the roll-out to begin before Christmas.

"We have formally asked the regulator to assess the Oxford/AstraZeneca vaccine, to understand the data and determine whether it meets rigorous safety standards," Hancock said in a statement.

"This letter is an important step towards deploying a vaccine as quickly as safely possible."

Britain's Medicines and Healthcare products Regulatory Agency (MHRA) is already assessing the vaccine in a "rolling review" as data comes in on safety and efficacy.

Hancock has also asked the MHRA to approve the Pfizer/BioNTech candidate after it was shown to be 95% effective.

Oxford and AstraZeneca published interim efficacy results on Monday, which showed that the vaccine could be 90% effective when given as a half dose followed by a full dose.

Questions have been raised about the Oxford/AstraZeneca data and the robustness of that result, though the MHRA approved the use of the half-dose/full-dose regime a subgroup received in the trial.

Britain's top science adviser said on Thursday that the interim results showed the Oxford/AstraZeneca vaccine worked.

"The headline result is the vaccine works and that's very exciting," Patrick Vallance said during a news conference with Prime Minister Boris Johnson. Chief Medical Officer Chris Whitty said it was up to the regulator to make an assessment.