Relapsed Refractory Acquired Thrombotic Thrombocytopenic Purpura (aTTP); This literature-non-study case was reported in a literature article and describes the occurrence of THROMBOTIC THROMBOCYTOPENIC PURPURA (Relapsed Refractory Acquired Thrombotic Thrombocytopenic Purpura (aTTP)) in a 57-year-old male patient who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 vaccination.       Previously administered products included for Thrombotic thrombocytopenic purpura: Rituximab, BORTEZOMIB (3 months of weekly bortezomib 1 mg/m^2), MYCOPHENOLATE MOFETIL (up-titrated to 1,750 mg twice daily, and then slowly tapered off over a 2-year.) and ECULIZUMAB. Past adverse reactions to the above products included No adverse event with BORTEZOMIB, ECULIZUMAB, MYCOPHENOLATE MOFETIL and Rituximab. Concurrent medical conditions included Thrombotic thrombocytopenic purpura since 2016.    On an unknown date, the patient received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On an unknown date,  after starting mRNA-1273 (Moderna COVID-19 Vaccine), the patient experienced THROMBOTIC THROMBOCYTOPENIC PURPURA (Relapsed Refractory Acquired Thrombotic Thrombocytopenic Purpura (aTTP)) (seriousness criteria hospitalization and medically significant). The patient was treated with DIPHENHYDRAMINE for Thrombotic thrombocytopenic purpura, at an unspecified dose and frequency; RITUXIMAB for Thrombotic thrombocytopenic purpura, at a dose of qwk for 4 weeks; CAPLACIZUMAB for Thrombotic thrombocytopenic purpura, at a dose of 11 milligram once a day; MYCOPHENOLATE MOFETIL for Thrombotic thrombocytopenic purpura, at a dose of 500 milligram twice a day; PREDNISONE for Thrombotic thrombocytopenic purpura, at an unspecified dose and frequency and CYCLOPHOSPHAMIDE (intravenous) for Thrombotic thrombocytopenic purpura, at a dose of 750 mg/m2 every three weeks. At the time of the report, THROMBOTIC THROMBOCYTOPENIC PURPURA (Relapsed Refractory Acquired Thrombotic Thrombocytopenic Purpura (aTTP)) had resolved.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On an unknown date, ADAMTS13 activity assay: t less than 5 percent ADAMTS13 activity level was t <5% (normal >/= 70%), less than 5 percent less than 5 percent and 52-59 percent ADAMTS13 activity level has reached 52-59%. On an unknown date, ADAMTS13 inhibitor screen assay: 1.5 positive ADAMTS13 inhibitor screen and titer of 1.5 (normal <0.4 and 11.4 inhibitor level was the highest that it had ever been at 11.4.. On an unknown date, Blood creatinine: baseline Baseline. On an unknown date, Blood lactate dehydrogenase (122-222): 508 u/l (Low) 508 U/L. On an unknown date, Blood smear test: 1-3 schistocytes per high-powered field 1-3 schistocytes per high-powered field. On an unknown date, Haemoglobin (13.2-16.6): 12.4 g/dl (Low) 12.4 g/dL. On an unknown date, Platelet count (135 x 10^9/l-317 x 10^9/l): 38 x 10^9/l (Low) 38 x 10^9/L, 200-300 x 10^9/l baseline of 200-300 x 10^9/L, normal platelets remained stable within the upper limit of normal during his 30 day course of caplacizumab, 23 x 10^9/l 3 weeks after completion of caplacizumab, he had an acute drop in his platelets to 23 x 10 9/L. and normal platelet count normalized and remain stable.     For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter considered THROMBOTIC THROMBOCYTOPENIC PURPURA (Relapsed Refractory Acquired Thrombotic Thrombocytopenic Purpura (aTTP)) to be related.    Concomitant medications were not reported. . The patient was initially diagnosed with aTTP, after presenting with symptoms of dark urine, mild headaches and transient episodes of aphasia and paresthesia. and was required prolonged and extensive treatment including over 5 weeks of daily therapeutic plasma exchange (TPE), followed by gradual reduction in frequency of TPE sessions. The patient was doing well for 3 years without manifestations of aTTP   Patient developed a petechial rash 7 week after Moderna COVID-19 vaccine and was referred to the emergency department and was admitted to the hospital, and initiated on daily TPE, with steroids and diphenhydramine prior to each TPE session. He quickly improved with TPE alone and was again hospitalized and underwent 8 sessions of daily TPE.; Sender's Comments: This case concerns a 57-year-old male patient with relevant medical history refractory acquired thrombotic thrombocytopenic purpura, who experienced the unexpected serious event of Relapsed Refractory Acquired Thrombotic Thrombocytopenic Purpura . The event occurred approximately 7 weeks after the second dose of mRNA-1273 (Moderna covid-19 vaccine). The patient was initially diagnosed with aTTP, after presenting with symptoms of dark urine, mild headaches and transient episodes of aphasia and paresthesia. and was required prolonged and extensive treatment including over 5 weeks of daily therapeutic plasma exchange (TPE), followed by gradual reduction in frequency of TPE sessions. Patient developed a petechial rash 7 week after Moderna COVID-19 vaccine and was referred to the emergency department and was admitted to the hospital, and initiated on daily TPE, with steroids and diphenhydramine prior to each TPE session. He quickly improved with TPE alone and was again hospitalized and underwent 8 sessions of daily TPE.. Laboratory reports showed platelets of 38 x 109/L, mildly elevated LDH (508 u/L), hemoglobin of 12.4 g/dL, creatinine at baseline, and peripheral blood smear showing 1-3 schistocytes per high-powered field, ADAMTS13 activity level was t <5% with positive ADAMTS13 inhibitor screen and titer of 1.5, consistent with diagnosis of relapsed aTTP. The rechallenge was not applicable as event occurred after second dose. This patient's underlying medical condition remains a confounder. The benefit-risk relationship of mRNA-1273 (Moderna covid-19 vaccine) is not affected by this report.