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The claim, where the mistake is acknowledged, comes days after the company and university called the vaccine “highly effective,” not to mention why some clinical trial participants did not receive the same amount of vaccine in the first of two injections, as expected, reports the AP agency.
Surprisingly, the group of volunteers who received a lower dose appeared to be much more protected than the volunteers who received two full doses.
In the low-dose group, AstraZeneca said, the vaccine appears to be 90 percent effective, while in the group that received two full doses, the effectiveness appears to be 62 percent.
With these combined results, the manufacturers revealed that the vaccine appears to be 70% effective, but how they were obtained has raised questions from experts.
The partial results announced on Monday are the result of ongoing mass clinical trials in the UK and Brazil aimed at determining the ideal dose of the vaccine, as well as examining its safety and efficacy.
Various combinations and doses were administered to the volunteers and the results were compared with others who received a meningitis vaccine or saline.
Before starting the tests, the researchers explained all the steps to follow and how to analyze the results. Any deviation from this protocol can compromise the results.
In a statement released today, the University of Oxford said some of the vials used in the test did not have the right concentration of the vaccine, meaning some volunteers received half a dose.
The university added that it had discussed the issue with regulators and agreed to complete the test. The production problem has been resolved, according to the statement.
For experts, the relatively low number of people in the low-dose group makes it difficult to understand whether the observed efficacy in the group is real or a statistical peculiarity.
About 2,741 people received a half dose of the vaccine followed by a full dose, AstraZeneca revealed, with a total of 8,895 people receiving both full doses.
Another factor at play is the fact that none of the participants in the low-dose group are older than 55, with younger people tending to have stronger immune responses than older adults.
As a discussion is still the union of the two participating groups who received different dosage levels to reach an average efficacy of 70%, pointed out one of the members of the Chatham House global health program, David Salisbury.
One of the Oxford scientists leading the investigation believes that maximum effectiveness in the group taking the reduced dose may be related to providing the exact amount of vaccine to trigger the best immune response.
“Not too little, not too much. Even a lot can give a low-quality response,” he said.
Details of the clinical trial results will be published in medical journals and provided to UK regulators, who will decide on the vaccine’s marketing authorization.
These reports will include a detailed analysis with demographic information or information on who got sick in each group, which will provide a more complete picture of the vaccine’s effectiveness.
The covid-19 pandemic has caused at least 1,415,258 deaths resulting from more than 60 million cases of the infection worldwide, according to a report made by the French agency AFP.
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