2nd COVID-19 vaccine trial paused over unexplained illness

A late-stage study of Johnson & Johnson’s COVID-19 vaccine candidate has been paused while the company investigates whether a study participant’s “unexplained illness” is related to the shot.

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...