New Brunswick-based Johnson & Johnson announced Monday that the company has paused a COVID-19 vaccine trial after a person in the study developed an unexpected illness.

The company did not release details or symptoms of the person’s illness, and only said that researchers are evaluating the subject to see if the illness is related to their medication.

Johnson & Johnson officials also emphasize that the person who got sick could have been taking the placebo. But they say that everything is on hold until more information can be gathered.