On June 5, researchers at the University of Oxford quietly made a change to a late-stage clinical trial of their COVID-19 vaccine. In an amendment noted in a document marked confidential, they said they were adding a new group of participants.
The adjustment might seem minor in a large-scale study. But it masked a mistake that would have potentially far-reaching consequences: Many of the United Kingdom trial subjects had inadvertently been given only about a half dose of the vaccine.
The new volunteers would now receive the correct dose. The trial continued.
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