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 was overtaken by U.S. drugmaker Pfizer, whose shots — with a success rate of around 95 percent — were administered to the U.K. 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 six percent of U.K. trial participants were given the lower dose regimen and none of them were 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 U.S. Food and Drug Administration.
Efficacy reflects how well a vaccine works in clinical trials. Effectiveness is how well a vaccine or a product will work in the real world rather than ideal settings.
Vaccine efficacy levels vary
COVID-19 vaccines from Pfizer and German partner BioNTech and from 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.”