"Following our guidelines, the participant's illness is being reviewed and evaluated by the ENSEMBLE independent Data Safety Monitoring Board (DSMB) as well as our internal clinical and safety physicians," the company said in a statement
. ENSEMBLE is the name of the study.
"Adverse events -- illnesses, accidents, etc. -- even those that are serious, are an expected part of any clinical study, especially large studies." The pause was first reported by Stat News.
Johnson & Johnson's Janssen vaccine arm is developing the shot. The company did not say what the unexplained illness was, but one point of clinical trials is to find out if vaccines cause dangerous side effects. Trials are stopped when they pop up while doctors check to see if the illness can be linked to the vaccine or is a coincidence.