Jan 11 (Reuters) - The U.S. Food and Drug Administration on Tuesday amended the fact sheet for Johnson & Johnson"s (JNJ.N) COVID-19 vaccine to include a rare risk of immune thrombocytopenia, a 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 regulator said in a letter to J&J"s arm, Janssen Biotech Inc. The symptoms include easy bruising or tiny blood spots under the skin, or unusual or excessive bleeding, the FDA said. The amendment fact sheet follows similar moves for the vaccine by other regulators, including that of European Medicines Agency in October. Both the J&J and AstraZeneca (AZN.L) vaccines, which are based on a similar platform, have previously been associated with another very rare combination of blood clotting and low platelet counts, known as thrombosis with thrombocytopenia syndrome. The U.S. Centers for Disease Control and Prevention had also last month recommended Americans choose to receive one of two other authorized COVID-19 vaccines from Pfizer-BioNTech (PFE.N), over J&J"s single-dose shot, due to the rare but sometimes fatal risk.