Then, on Tuesday, Moncef Slaoui, the head of Operation Warp Speed, the U.S. initiative to fast-track coronavirus vaccines, noted another limitation in AstraZeneca’s data. On a call with reporters, he suggested that the participants who received the half-strength initial dose had been 55 years old or younger.
Mr. Pangalos confirmed that on Wednesday, saying the participants received the half-strength dose over a matter of weeks before the error was discovered.
The fact that the initial half-strength dose wasn’t tested in older participants, who are especially vulnerable to Covid-19, could undermine AstraZeneca’s case to regulators that the vaccine should be authorized for emergency use.