The FDA revised the fact sheet for Johnson & Johnson's COVID-19 vaccine Jan. 11 to include new information about the risk of a rare bleeding disorder.
"Reports of adverse events following use of the Janssen COVID-19 vaccine under emergency use authorization suggest an increased risk of immune thrombocytopenia during the 42 days following vaccination," the FDA said in a letter to Janssen Biotech, J&J's biotech arm.
Immune thrombocytopenia can cause easy or excessive bruising and bleeding, though the FDA said the chance of developing this disorder after vaccination is very low.
The new warning comes about a month after the CDC recommended Americans receive Pfizer or Modern's COVID-19 vaccine over Johnson & Johnson's due to concerns about the rare risk of blood clots following the shot.
Read the full letter here.