Questions about the vaccine: The United States has ordered 300 million doses of the two-dose candidate vaccine, which faced doubts during development. A final-stage trial was interrupted this fall to assess a serious reaction to an injection, while the promising results of an early injection reading were attributed to a dosing error.
Slaoui said that while the AstraZeneca vaccine appears to be very effective against serious illnesses, its effectiveness among the elderly is “effectively unknown” because few elderly people were enrolled at the start of the trial. He said it remains his biggest question about the company’s injection, given the virus’s impact on the elderly.
British regulators on Wednesday morning were the first in the world to authorize the use of the AstraZeneca vaccine. Rather than withholding doses to ensure people receive a second injection quickly, British health officials said they would vaccinate the country extensively with the first doses and provide the second within three months. They said the move would provide some level of protection for the entire country amid growing infections and a new variant of the virus that appears to be more transmissible.
But the effectiveness of the AstraZeneca vaccine is still unclear, especially when doses are spaced. The AstraZeneca vaccine so far has shown 62 percent effectiveness when used in two full doses given 28 days apart. But after a dilution error in one arm of a phase 3 trial, scientists found that the vaccine was 90 percent effective when a small group received half a dose first.
US regulators need more evidence: The drugmaker said the combined results showed 70 percent effectiveness, but Slaoui suggested that US regulators would not be satisfied with that finding.
“As far as the American people are concerned, I think it’s important to say that one vaccine is 95 percent effective, another vaccine is X percent, whatever that number is,” Slaoui told reporters, referring to the high efficacy rates of Pfizer and BioNTech and Modern Vaccines that the FDA has authorized. “We need a clear and concrete number more than a number that is accumulated by adding different tests with different schedules and different materials.”
Slaoui also questioned Britain’s dosing strategy. He said it is possible that a booster injection would be more effective when given months later, but said the UK decision was based on theory, not evidence.
“It is important, I think, to use the vaccine based on how you studied it,” he said.