AstraZeneca and Oxford University have given conflicting accounts of how they came upon the most effective dosing pattern for their COVID-19 vaccine, a rare instance of public dissension between major institutions collaborating on a pivotal project.
The discrepancy centers on the regimen administered to a smaller group of volunteers in the late-stage trials, of half a dose followed by a full dose. This diverged from the original plan of two full doses, given to the majority of participants.
The half-dose pattern was found to be 90% effective, versus the 62% success rate of the two-full-dose main study, based on interim data.