Hemolytic anemia exacerbation; This literature-non-study case was reported in a literature article and describes the occurrence of HAEMOLYTIC ANAEMIA (Hemolytic anemia exacerbation) in a 38-year-old female patient who received mRNA-1273 (Spikevax) for COVID-19 prophylaxis.   LITERATURE REFERENCE:      Concurrent medical conditions included Paroxysmal nocturnal hemoglobinuria (chronic paroxysmal nocturnal hemoglobinuria). Concomitant products included RAVULIZUMAB for Paroxysmal nocturnal hemoglobinuria.  On an unknown date, the patient received second dose of mRNA-1273 (Spikevax) (unknown route) 1 dosage form. On an unknown date, the patient experienced HAEMOLYTIC ANAEMIA (Hemolytic anemia exacerbation) (seriousness criteria hospitalization and medically significant). At the time of the report, HAEMOLYTIC ANAEMIA (Hemolytic anemia exacerbation) had resolved.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On an unknown date, Blood bilirubin: 4.7 mg/dl Elevated. On an unknown date, Chest X-ray: Chest x-ray did not demonstrate any evidence of infection or pleural effusions. On an unknown date, Full blood count: 5.9 g/dL Initial complete blood count showed a hemoglobin of 5.9 g/dL,compared to her baseline of 9 without any evidence of bleeding.. On an unknown date, Haemoglobin: On treatment, patient achieved stable hemoglobin levels. On an unknown date, Haptoglobin: <20 mg/dl. On an unknown date, Physical examination: Patient was hemodynamically stable on admission and afebrile. Physical exam revealed generalized lethargy/weakness and jaundice.. On an unknown date, Reticulocyte count: 295.2 x 10^9 mg/dl Elevated.   For mRNA-1273 (Spikevax) (Unknown), the reporter considered HAEMOLYTIC ANAEMIA (Hemolytic anemia exacerbation) to be related.    Patient presented with 3 days of generalized fatigue, chills, and worsening scleral icterus. She reports being unable to move out of the bed with concomitant somnolence.  Of note, she received her second dose of the Moderna COVID-19 vaccine 2 days prior to symptom onset and not had any similar symptoms prior to this episode.  Patient received a total of 3 units of packed red-blood cells with subsequent stable hemoglobin levels and did not require emergent use of glucocorticoids or plasma exchange. Her lethargy improved slowly, and within a week, she returned back to her baseline functional status. She was ultimately stable and discharged for follow up with her hematologist without any complications.  Authors noted that given the timing of the onset of the patient's symptoms, it was highly suggestive that patient's second COVID-19 vaccination was the inciting factor for her acute hemolytic anemia.  Company Comment: This literature-non-study case, concerns a female patient aged 38 years, with relevant medical history of chronic paroxysmal nocturnal hemoglobinuria on maintenance ravculizumab therapy reported, who experienced the unexpected serious (Hospitalization/medically significant) event of Haemolytic anaemia (reported as Hemolytic anemia exacerbation) that occurred two days after second dose of mRNA-1273 vaccination in covid-19 vaccination series. Patient presented to hospital with 3 days history of generalized fatigue, chills and worsening scleral icterus along with somnolence. She was hemodynamically stable and afebrile on admission. Physical exam revealed generalized lethargy/weakness and jaundice. Chest x-ray done ruled out infection or pleural effusions. Initial complete blood count showed a hemoglobin of 5.9 g/dL, compared to her baseline of 9 without any evidence of bleeding. Absolute reticulocyte and bilirubin levels were elevated to 295.2 x 109 and 4.7 mg/dL respectively with a haptoglobin of <20mg/dL. She received a total of 3 units of packed red-blood cells with subsequent stable hemoglobin levels and did not require emergent use of glucocorticoids or plasma exchange. Her symptoms improved slowly within a week, was stable at the time of discharge without any complications. Relevant medical history remains a confounder to the event. The benefit-risk relationship of mRNA-1273 is not affected by this report.; Sender's Comments: This literature-non-study case, concerns a female patient aged 38 years, with relevant medical history of chronic paroxysmal nocturnal hemoglobinuria on maintenance ravculizumab therapy reported, who experienced the unexpected serious (Hospitalization/medically significant) event of Haemolytic anaemia (reported as Hemolytic anemia exacerbation) that occurred two days after second dose of mRNA-1273 vaccination in covid-19 vaccination series. Patient presented to hospital with 3 days history of generalized fatigue, chills and worsening scleral icterus along with somnolence. She was hemodynamically stable and afebrile on admission. Physical exam revealed generalized lethargy/weakness and jaundice. Chest x-ray done ruled out infection or pleural effusions. Initial complete blood count showed a hemoglobin of 5.9 g/dL, compared to her baseline of 9 without any evidence of bleeding. Absolute reticulocyte and bilirubin levels were elevated to 295.2 x 109 and 4.7 mg/dL respectively with a haptoglobin of <20mg/dL. She received a total of 3 units of packed red-blood cells with subsequent stable hemoglobin levels and did not require emergent use of glucocorticoids or plasma exchange. Her symptoms improved slowly within a week, was stable at the time of discharge without any complications. Relevant medical history remains a confounder to the event. The benefit-risk relationship of mRNA-1273 is not affected by this report.