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The high efficacy of the coronavirus vaccine candidate from AstraZeneca and the University of Oxford could be partly due to a dosing error.
In the vaccine effectiveness press release released on Monday, the vaccine was more effective – up to 90% – in the group that received a half dose and then a full dose.
But the candidate vaccine was only 62% effective in the group that received two full doses.
Mene Pangalos, head of biopharmaceutical research and development at AstraZeneca, admitted to Reuters on Monday that some participants were given a half dose and then a full dose due to a dosing error.
Pangalos called it a “useful mistake” in a subsequent interview with the New York Times, published Wednesday.
The University of Oxford said in a statement on Wednesday that some of the vials in the trial did not have the correct concentration of vaccine. The university said the issue had been discussed with regulators and they decided to complete the advanced stage trial in two groups, according to the AP.
Experts say the small number of people in the low-dose group – some 2,741 – makes it difficult to know whether the effectiveness is a statistical oddity.
Also, none of the people in the low dose group were over 55 years old, and younger people tend to have a stronger immune response than those who are older.
David Salisbury, associate member of the Global Health Program at Chatham House, said another area of confusion is that the press release pooled the results of the two groups to achieve an average efficiency of 70%.
“You took two studies where different doses were used and you found a composite that didn’t represent any of the doses,” Salisbury told the AP. “I think a lot of people have problems with that.”
Researchers say that a smaller first dose might be more effective because you need the right amount for a good immune response.
Some have criticized AstraZeneca and Oxford for their lack of transparency in the publication of the results.
“Astrazeneca / Oxford get a low mark for transparency and thoroughness in the vaccine trial results they reported. It’s not like Pfizer or Moderna where we had the protocols up front and a Pre-specified primary analysis has been reported, “Natalie Dean, assistant professor of biostatistics at the University of Florida.
“If they’re looking to get half-dose approved, they would have to wait until they get a convincing result. Otherwise, we may end up in a ‘limbo of evidence’.”
More detailed trial results should be provided to regulatory authorities who will decide whether or not to authorize the vaccine.
Moncef Slaoui, who heads the U.S. coronavirus vaccination program, said in a call with reporters that U.S. officials were trying to determine what immune response the vaccine produced.
They could decide to modify the AstraZeneca study in the United States to include a half dose: “But we want it to be based on data and on science,” he said.
Euronews has contacted AstraZeneca and the University of Oxford for their comments.
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