WASHINGTON (AP) — U.S. health officials say Johnson & Johnson’s COVID-19 vaccine may pose a “small possible risk” of a rare but potentially dangerous neurological reaction.

The Centers for Disease Control and Prevention (CDC) said Monday that it has received reports of 100 people who got the shot developing an immune system disorder that can cause muscle weakness and occasionally paralysis.

The reports represent a tiny fraction of the nearly 13 million Americans who have received the one-dose vaccine.

The New York Times and The Washington Post report that the Food and Drug Administration is planning to warn that the J&J vaccine can lead to an increased risk of a rare neurological condition known as Guillain–Barré syndrome.

The Mayo Clinic describes the syndrome as a rare disorder in which your body’s immune system attacks your nerves. The organization said weakness and tingling in your extremities are usually the first symptoms, and that the sensations can quickly spread, eventually paralyzing your body.

The government said the vaccines most used in the U.S., made by Pfizer and Moderna, show no risk of the disorder.