The British pharmaceutical group AstraZeneca said it had found "the winning formula" to improve its COVID-19 vaccine developed with Oxford University.
The British laboratory announced in November that its vaccine was on average 70 per cent effective in clinical trials compared with more than 90 per cent for vaccines by Pfizer/BioNTech and Moderna, which have both been already authorised for use in several countries.
The interim clinical trial results showed large differences in the data because of two different protocols: the efficacy was 90 per cent for volunteers who first received a half dose and then a full dose one month later, but only 62 per cent for another group vaccinated with two full doses.
The results had been criticised because the injection of a half-dose was due to an error and a relatively small group had followed this protocol. The company then announced that its vaccine required "an additional study".
But Pascal Soriot, chief executive of AstraZeneca, assured that the company's vaccine provided "100% protection" against severe forms of Covid-19, telling the Sunday Times newspaper: "We think we have figured out the winning formula and how to get efficacy that, after two doses, is up there with everybody else".
He added: "I can't tell you more because we will publish at some point".
The Oxford University/AstraZeneca vaccine is eagerly awaited in the UK because it is relatively inexpensive and can be stored in conventional freezers, unlike the Pfizer/BioNTech vaccine which must be stored at -70 degrees.
This makes it easier to vaccinate on a large scale as well as in retirement homes.
The UK, the first Western country to authorise the Pfizer/BioNTech vaccine for distribution in early December, is counting on this second vaccine to gain momentum and stop the surge in cases attributed to a new variant of the coronavirus on its soil.
"For the time being, we believe that the vaccine should remain effective" against the new variant, Soriot said. "But we can't be sure, so we're going to test it".
He assured that new versions were being prepared just in case, while hoping not to need them: "You have to be prepared".
The UK government announced on Wednesday that it had submitted full data on the Oxford University/AstraZeneca vaccine to the UK regulator, the Medicines and Healthcare products Regulatory Agency (MHRA).
According to the British press, the MHRA is due to make a decision in the next few days with a view to injecting the vaccine from January 4 onwards.
The UK has ordered 100 million doses of Oxford University/AstraZeneca vaccine, 40 million doses of which are due to be available by the end of March.
In all, the UK government has ensured access to more than 350 million doses by the end of next year, by sourcing from seven manufacturers during the clinical trial phase.
In total, more than 600,000 people have already received a first dose of the Pfizer/BioNTech vaccine.
The success of the current campaign in the UK is all the more crucial as the country, one of the most affected by the pandemic with more than 70,000 deaths, is seeing a resurgence of the virus.
The authorities have attributed this resurgence to a mutation which, according to a British study, is 50 per cent to 74 per cent more contagious and led to more than 40 countries closing their borders to UK travellers.