AstraZeneca has paused it’s COVID-19 vaccine trials because of a serious adverse reaction in a volunteer in the UK.

They came down with an inflammatory syndrome called transverse myelitis, which interrupts messages the spinal cord nerves send throughout the body.

AstraZeneca says it’s not abnormal to see unexplained illnesses in the trials, and they are not saying whether the sudden illness is officially from the vaccine or not as of yet.