The statement describing the error comes after the announcement on Monday that the shots were “highly effective” and made no mention of why some study participants didn’t receive as much vaccine in the first of two shots as expected.
Also, the Monday announcement did not present results from a single, large-scale, Phase 3 clinical trial, as was the case for earlier announcements about the BNT-Pfizer and Moderna vaccine, reports Wired.
The data from the AstraZeneca-Oxford study actually came from two studies, one conducted in the UK that began in May, and the second study, conducted in Brazil that began at the end of June. The studies were substantially different from each other.
There were no standardized dosing protocols across the trials and multiple combinations of doses of the vaccine were tried on the volunteers. Additionally, they did not provide the same “control” injections to volunteers who were not getting the experimental Covid vaccine.
Some of the volunteers in the control groups were given a meningitis vaccine while others got a saline shot, according to the Associated Press,
But the way in which the results were arrived at and reported by the companies has led to pointed questions from experts. The fact that they may have had to combine data from two trials in order to get a strong enough result raises the first red flag.
David Salisbury an associate fellow of the global health program at the Chatham House think tank said: “You’ve taken two studies for which different doses were used and come up with a composite that doesn’t represent either of the doses,″ he said of the figure. “I think many people are having trouble with that.″
Another interesting issue is that some volunteers were only given half a dose of the experimental vaccine, according to the AstraZeneca statement on Wednesday. This was because some of the vials used in the trial didn’t have the right concentration of vaccine.
The university said that it discussed the problem with regulators, and agreed to complete the late-stage trial with two groups. The manufacturing problem has been corrected, according to the statement, reports the Chicago Tribune.
The head of the U.S. coronavirus vaccine program Operation Warp Speed, Moncef Slaoui, said Tuesday in a call with reporters that U.S. officials are trying to determine what immune response the vaccine produced, and may decide to modify the AstraZeneca study in the U.S. to include a half dose.