The company said in a statement Monday evening that illnesses, accidents and other so-called adverse events “are an expected part of any clinical study, especially large studies,” but that its physicians and a safety monitoring panel would try to determine what might have caused the illness.
The pause is at least the second such hold to occur among several vaccines that have reached large-scale final tests in the U.S.
The company declined to reveal any more details about the illness, citing the participant’s privacy.
Temporary stoppages of large medical studies are relatively common. Few are made public in typical drug trials, but the work to make a coronavirus vaccine has raised the stakes on these kinds of complications.