Johnson & Johnson added a warning to the label for the company’s Covid-19 vaccine, cautioning that there was a risk of people developing a nerve disorder after getting the shot. Cases of the syndrome, have been seen in some people who got the J&J Covid-19 vaccine.

According to the Centers for Disease Control and Prevention Health authorities have found about 100 reports of the disorder among the 12.8 million people in the U.S. who have taken the shot. The agency added that most of the reports came two weeks after vaccination among men 50 years and older.

The warning label says that most cases appeared within 42 days of vaccination. Guillain-Barré is a rare side effect of some other vaccines, and occurs very rarely in the general population. Reports indicate that People can have trouble walking up stairs.

Other symptoms include difficulty with facial movements like speaking or swallowing, double vision and trouble controlling bladder or bowel function. In some cases, the syndrome can be life-threatening if paralysis spreads throughout the body or if it affects critical bodily functions like breathing, blood pressure or heart rate.