The scientists claimed that the vaccine’s highest success rate of 90 percent was only tested in people under the age of 55, raising fears that it might not work well in older people.
AstraZeneca, which has developed the vaccine with the University of Oxford, has launched the new trial which is expected to be completed quickly, without affecting the launch of the vaccine.
The Australian government has pledged to purchase 33.8 million doses of the vaccine.
The new trial should not delay delivery of the vaccine in Australia.
US vaccine czar Moncef Slaoui told reporters on Wednesday that they were reviewing vaccine data, as the robustness of the findings could suffer, as young people often produce stronger immune responses to vaccines.
Other aspects of the trial data have also raised concern among scientists, with the drug manufacturer at the time not explaining why they used two different dosing regimens and why the study group size was significantly smaller than the other. .
In one group, 2,741 participants received a half dose of the vaccine and then a full dose at least a month later. This group was 90 percent protected against COVID-19.
In the second group, 8,895 participants received a full dose followed by another full dose at least one month later. This group was only 62% protected.
Therefore, the vaccine is said to have an average efficacy of 70%.
An AstraZeneca spokesperson told CNN yesterday that “given the high efficacy we have now seen with the different dosing regimens, it is very important to further investigate these findings to establish the most effective dosing regimen for the vaccine.”
One point of confusion emerged on Tuesday, when AstraZeneca Executive Vice President Mene Pangalos told Reuters that a laboratory error was the reason some volunteers had received a lower dose.
“The reason we take half the dose is chance,” Pangalos said, adding that the researchers “had underestimated the dose of the vaccine by half.”
Oxford’s communications manager for vaccines told CNN on Wednesday that “dose selection for any new vaccine is a tricky area, and in exploring dose selection methods, we found that one gave a lower dose of The expected”.
Oxford said yesterday that a “difference in the manufacturing process” had led to the error.
A UK regulator overseeing the trial has agreed to include “both approaches” in Phase 3, the statement said.
Pangalos told the Wall Street Journal on Wednesday that the error was “really irrelevant.”
“We still have an efficacy that meets approval thresholds with a vaccine that is more than 60 percent effective,” he said.
But Dr. Saad Omer, a vaccine specialist at Yale School of Medicine, believes that the group with a 90 percent efficacy rate is relatively small, and that the results may not hold when more people receive this regimen.
“I hate criticizing my fellow academics, or anyone else,” he said.
“But spreading information like this is like asking us to try to read the tea leaves.”
Astrazeneca’s shares have fallen more than 6 percent since its announcement on Monday.