The Centers for Disease Control and Prevention on Monday confirmed 100 preliminary reports of Guillain-Barré syndrome, a rare neurological disorder, among the 12.8 million doses administered of J&J vaccine.

“These cases have largely been reported about two weeks after vaccination and mostly in males, many aged 50 years and older,” the CDC said in a statement.

Johnson and Johnson said it has discussed the reports with federal regulators at the Food and Drug Administration.

“The chance of having this occur is very low, and the rate of reported cases exceeds the background rate by a small degree,” the company said in a statement released Monday.

Similar issues have not been reported tied to Pfizer or Moderna.

Guillain-Barré syndrome is a rare disorder that occurs when a person’s immune system damages nerve cells and causes muscle weakness or paralysis.

Most people recover fully although some will report long-term nerve damage.

According to the CDC, the majority of people who develop GBS report the symptoms after having a respiratory illness, including the flu, or getting sick with diarrhea. One common cause is a bacteria tied to eating uncooked poultry.

It’s also linked to vaccination, though rare, and is why the CDC monitors reports of GBS each flu season.

The CDC estimates there is one to two additional GBS cases per million doses of flu vaccine administered.