The Centers for Disease Control and Prevention (CDC) received reports that 100 people who got the Johnson & Johnson COVID-19 vaccine developed Guillain-Barre syndrome, a rare autoimmune disorder where one's own immune system attacks the nerves, causing muscle weakness and sometimes paralysis.

These reported cases only represent a fraction of the nearly 13 million Americans who received the vaccine. Most cases occurred in men age 50 and over about two weeks after their received their single dose, the CDC said in a statement.