SINGAPORE - Late-stage human trials for the Covid-19 vaccine candidate developed by Oxford University and biopharmaceutical company AstraZeneca showed that the vaccine could be up to 90 per cent effective, the company said on Monday (Nov 23).
A lower dose appeared to be more effective, preliminary results showed.
Under the dosing regimen where volunteers were first given half a dose of the vaccine, followed by a full dose at least one month apart, efficacy was 90 per cent.
But when volunteers were given two full doses at least one month apart, efficacy was 62 per cent.
The combined analysis from both dosing regimens involving more than 11,000 volunteers resulted in an average efficacy of 70 per cent, AstraZeneca said in a statement.
More data will continue to accumulate and additional analysis will be conducted, it added. This will help to improve the efficacy reading and establish the duration of protection.
Professor Andrew Pollard, chief investigator of the Oxford vaccine trial at the university, said the findings showed that the vaccine was effective.
"Excitingly, we've found that one of our dosing regimens may be around 90 per cent effective and if this dosing regime is used, more people could be vaccinated with planned vaccine supply," he added.
In September, AstraZeneca stopped trials of the vaccine after a person who was involved got sick. The trials were later allowed to resume.
Severe adverse events occur when a volunteer in a vaccine trial ends up in hospital, even if it was due to other causes, like a road traffic incident. When such events happen, an independent body of experts steps in to review the data to decide if the severe adverse event was caused by the experimental vaccine or was completely unrelated.
AstraZeneca said in Monday's statement that no serious safety events related to vaccine had been confirmed, and that it was well tolerated across both dosing regimens.
The British drugmaker said it will have as many as 200 million doses by the end of 2020, around four times as many as US competitor Pfizer. Seven hundred million doses could be ready globally as soon as the end of the first quarter of 2021.
The latest update from AstraZeneca comes after Pfizer and Moderna - the firms behind two other Covid-19 vaccine frontrunners - revealed positive preliminary results from their own late-stage trials.
Pfizer said on Nov 18 that final results from the late-stage trial of its Covid-19 vaccine show it was 95 per cent effective, while Moderna on Nov 16 said preliminary data showed its vaccine was 94.5 per cent effective in preventing Covid-19.
Pfizer submitted an application to the US Food and Drug Administration on November 20 for an emergency use authorisation of the vaccine and Moderna is planning a similar move.
Speaking at a virtual press conference on Monday (Nov 23), Prof Pollard said it was difficult to explain the differences in the results in the absence of published data sets for the different vaccines.
"We don't know exactly what everyone is measuring in the trials until we've actually got those full data sets out and we can see exactly what everyone has," he said, adding that the researchers behind the Oxford and AstraZeneca vaccine plan to submit their own data for publication in the days ahead.
Oxford University's Professor Sarah Gilbert added that the world would need multiple vaccines, because no one developer or manufacturer will be able to produce enough doses to meet global demand.
She added: "It's really excellent to see that the high efficacy that we're now getting out of these trials - coupled with the safety, the ability to manufacture in large doses, the ability to feed into existing distribution networks for vaccines that already are in place around the world - because all of that together is going to to really make a difference to get a lot of people vaccinated."