Johnson & Johnson has put its COVID-19 vaccine trial on hold after a participant in the phase III study developed an unexplained illness.

Following the patient illness, J&J said that an independent data and safety monitoring board (DSMB) will investigate the event.

As a result, J&J has paused recruitment to the phase III trial, which is aiming to recruit up to 60,000 people.

The exact details of the illness are still unknown, with J&J saying that it cannot release more information because of privacy reasons.

We must respect this participant’s privacy. We’re also learning more about this participant’s illness, and it’s important to have all the facts before we share additional information,” J&J added in a statement.

In a statement, the company said that adverse event – such as the one that has occurred in the vaccine trial – are an expected part of any study and especially in large-scale studies.

J&J’s trial is on a study pause as opposed to a regulatory hold – a regulatory hold of a clinical trial is a requirement by a regulatory health authority, such as the US Food and Drug Administration.

A study pause, on the other hand, is a standard component of a clinical trial protocol. Typically, study pauses are not communicated publicly, only to the study investigators.

In September, AstraZeneca paused global studies of its COVID-19 vaccine candidate after a patient developed transverse myelitis, an inflammation of the spinal cord.