The COVID-19 vaccine participant whose unexpected illness put the AstraZeneca trials on pause came down with an inflammatory syndrome known as transverse myelitis, according to a report.

The individual had been involved in the UK trials when they came down with the condition, which affects the spinal cord and is often sparked by viral infections, a source told The New York Times.

The illness results in inflammation of both sides of the spinal cord, interfering with how messages are sent throughout the body and potentially causing paralysis, according to the Mayo Clinic.

It’s also associated with pain, muscle weakness, sensory problems, or bladder and bowel dysfunction.