After dramatic rebuke, AstraZeneca lowers vaccine efficacy estimate—a little

Enlarge / A vial of the AstraZeneca/Oxford vaccine is pictured at a coronavirus vaccination center at the Wanda Metropolitano stadium in Madrid on March 24, 2021. (credit: Getty | Gabriel Bouys)

Brushing aside a dramatic rebuke from government researchers and independent experts, AstraZeneca on Wednesday night announced that a new analysis found its COVID-19 vaccine to be 76 percent effective at preventing symptomatic COVID-19-down from the 79 percent efficacy estimate it announced in a press release Monday.

The new estimate is still high, according to an independent board of experts tasked with overseeing the vaccine's trial and data analysis. The trial's Data and Safety Monitoring Board (DSMB) sent a highly unusual letter to AstraZeneca soon after the Monday press release, noting that trial data it had seen during February and March meetings suggested that the vaccine's efficacy was actually between 69 percent and 74 percent.

The DSMB is concerned that AstraZeneca chose to use data that was already outdated and potentially misleading in their press release," the letter stated. The point that is clear to the board is that the [vaccine efficacy number]... they chose to release was the most favorable for the study as opposed to the most recent and most complete. Decisions like this are what erode public trust in the scientific process."

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