LONDON - AstraZeneca and Oxford University have more work to do to confirm whether their COVID-19 vaccine can be 90 percent effective, peer-reviewed data published in The Lancet showed on Tuesday, potentially slowing its eventual rollout in the fight against the pandemic.
Once seen as the frontrunner in the development of a vaccine against the coronavirus crisis, the British team were overtaken by US drugmaker Pfizer, whose shots - with a success rate of around 95 percent - were administered to UK pensioners on Tuesday in a world-first hailed as V-Day.
Detailed results from the AstraZeneca/Oxford trials have been eagerly awaited after some scientists criticized a lack of information in their initial announcement last month.
However, the Lancet study gave few extra clues about why efficacy was 62 percent for trial participants given two full doses, but 90 percent for a smaller sub-group given a half, then a full dose.
"(This) will require further research as more data becomes available from the trial," the study said.
Less than 6 percent of UK trial participants were given the lower dose regimen and none of them was aged over 55, meaning more research will be needed to investigate the vaccine's efficacy in older people who are particularly susceptible to COVID-19.
Pooling the results, overall efficacy was 70.4 percent, the data on Tuesday showed. That is above the 50 percent minimum set by the US Food and Drug Administration.
COVID-19 vaccines from Pfizer/BioNTech and Moderna have reported efficacy levels of more than 90 percent in late stage trials.
But the AstraZeneca/Oxford vaccine is seen as particularly important to tackling the pandemic in the developing world, as it would be cheaper and easier to distribute.
"The basic message that the overall efficacy across the trials that are reported here is about 70 percent but with a clear description of its uncertainty," said Stephen Evans, a professor of pharmacoepidemiology at the London School of Hygiene & Tropical Medicine.
"The statistical uncertainty is that the efficacy could be as low as 55 percent or as high as 80 percent. The Pfizer/BioNTech and Moderna vaccines both have efficacies above 90 percent and are clearly more efficacious under trial conditions."
Asked whether the half, then full dose regimen had been a mistake, Andrew Pollard, director of the Oxford Vaccine Group and chief investigator into the trials, told a news conference it had been "unplanned."
Head of AstraZeneca's non-oncology research and development, Mene Pangalos, said he hoped requests for approval from regulators around the globe could still be submitted this year.
"We hope that once the regulatory authorities review the data, we can get approval any time from the completion of the submission, which could be any time from the end of this year to early next year," he said.
However, Pollard conceded the different results from the two dosage regimens complicated matters.
"The regulators will decide exactly what their label should say," he said, when asked whether regulators might approve the two full shots regiment first, and then potentially the half, then full, shot regiment when more data is in.
Pangalos also said he assumed U.S. regulators would want to see results from an ongoing trial in the United States before giving their approval.
The Oxford researchers said the vaccine was found to be safe, with three out of the roughly 23,700 participants experiencing serious conditions that were possibly related to either the COVID-19 vaccine or a standard meningitis vaccine given to a control group.
A case of a serious neurological illness, transverse myelitis, was reported 14 days after a COVID-19 vaccine booster shot, which was "possibly related to vaccination," they said.
This case had led to a seven-week trial suspension in the United States and to brief halts in trials in other countries.
A case of fever above 40°C occurred in South Africa, but it was not disclosed whether this participant received the vaccine because the person recovered quickly and is continuing the trial without knowledge of the shot received, as is the norm.