The head AstraZeneca says researchers believe the drugmaker's coronavirus vaccine will be effective against a new COVID-19 variant driving a rapid infections surge in Britain.
Chief executive Pascal Soriot has also told the Sunday Times developers have figured out a "winning formula" making the shot as effective as rival candidates.
Some have raised concern the jab, which is being developed with Oxford University and expected to win UK approval this week, may not be as good as Pfizer's which is already being distributed in Britain and elswhere.
Partial results suggest the shot is about 70 per cent effective for preventing illness from coronavirus infection, compared to the 95 per cent efficacy reported by Pfizer and German partner BioNTech.
"We think we have figured out the winning formula and how to get efficacy that, after two doses, is up there with everybody else," Soriot said.
"I can't tell you more because we will publish at some point."
Britain's government says its medicines regulator is reviewing the final data from AstraZeneca's phase three clinical trials.
The Times and others have reported that the green light could come by Thursday and the vaccines can start to be rolled out for the UK public in the first week of January.
Asked about the vaccine's efficacy against the new virus variant spreading in the UK, Soriot said: "So far, we think the vaccine should remain effective but we can't be sure, so we're going to test that."
British authorities have blamed the variant for soaring infection rates across the country. They say it is much more transmittable but there is no evidence it makes people more ill.
Prime Minister Boris Johnson sounded an urgent alarm about the variant before Christmas, saying it was spreading rapidly and plans to travel and gather must be cancelled for millions to curb its spread.
Authorities have since put increasing areas of the country - affecting about 24 million people or 43 per cent of the population - in the strictest level of restrictions.
Nonessential shops have closed, restaurants and pubs can only operate for takeout and no indoor socialising is allowed.
Many countries swiftly barred travel from the UK but variant cases have since also been reported in a dozen locations around the world.
Health officials said on December 24 more than 600,000 people had received the first of two doses of the Pfizer vaccine.
Britain recorded another 30,501 positive COVID-19 cases and a further 316 deaths on Sunday, bringing the country's total death toll to 70,752.