Johnson & Johnson has temporarily paused its COVID-19 vaccine clinical trials in the US due to an unexplained illness in a participant.

The participant’s illness is being reviewed and evaluated by an independent data and safety monitoring board as well as the company’s clinical and safety physicians, Johnson & Johnson said in a statement.

Stat News reported the pause earlier in the day citing a document sent to outside researchers running the 60,000-patient clinical trial.

The document stated that a “pausing rule” had been met, the online system used to enrol patients in the study had been closed and the data and safety monitoring board would be convened.