The boss at the firm behind the United Kingdom's Oxford coronavirus vaccine believes it has found the "winning formula" to improve the jab's efficacy.
The British government has ordered 100 million doses of the AstraZeneca-partnered vaccine, with around 40 million available by the end of March.
There have been some concerns it may not be as good at preventing symptomatic disease as others already being distributed such as the one by Pfizer.
"We think we have figured out the winning formula and how to get efficacy that, after two doses, is up there with everybody else," AstraZeneca chief Pascal Soriot said on Saturday.
"I can't tell you more because we will publish at some point."
Soriot told The Sunday Times newspaper of the figures already released on the jab.
"We would have preferred a simpler set of results but overall we thought these are positive, they meet the criteria established by regulators around the world," he said.
"We assumed people would be a bit disappointed, that's for sure but didn't expect that storm."
His comments come as London's Sunday Telegraph reports the Oxford jab could be rolled out en masse from a few days into the New Year.
According to the newspaper, the government hopes the approval could mean more than two million Brits receive their first vaccine dose within a fortnight, with the Oxford medicine available from January 4.
"The medicines regulator is reviewing the final data from the University of Oxford/AstraZeneca phase three clinical trials to determine whether the vaccine meets their strict standards of quality, safety and effectiveness," a government spokesman said.
"We must now give the MHRA time to carry out its important work and wait for its advice."