The fact sheet for Johnson & Johnson’s Covid-19 vaccine has been revised by U.S. regulators to warn of the risk of a rare bleeding disorder.

The Food and Drug Administration said in a letter to the company on Tuesday that adverse-event reports suggested an increased risk of immune thrombocytopenia, or ITP, during the 42 days following vaccination. Symptoms include bruising or excessive or unusual bleeding, according to the agency.

The changes to the fact sheet include recommendations to vaccination providers about giving the J&J shot to people with existing medical conditions, including those who have a low level of platelets, a type of blood cell that helps stop bleeding.

J&J said in a statement that “individuals who have been previously diagnosed with ITP should talk to their health-care provider regarding the risk of ITP and the potential need for platelet monitoring following vaccination.”

J&J’s vaccine has also been previously connected to rare but serious blood clots, a condition called thrombosis with thrombocytopenia syndrome, or TTS. Women ages 30 to 49 were at the highest risk, according to the Centers for Disease Control and Prevention.

So far, about 17 million Americans have been given the one-dose vaccine. Last month, the CDC recommended messenger RNA vaccines made by Moderna Inc. and Pfizer Inc. for use in adults over J&J’s shot.