hyperinflammatory syndrome; breakthrough COVID-19 infection; Hemophagocytic lymphohistiocytosis; This literature-non-study case was reported in a literature article and describes the occurrence of MULTISYSTEM INFLAMMATORY SYNDROME IN ADULTS (hyperinflammatory syndrome), COVID-19 (breakthrough COVID-19 infection) and HAEMOPHAGOCYTIC LYMPHOHISTIOCYTOSIS (Hemophagocytic lymphohistiocytosis) in a 63-year-old female patient who received mRNA-1273 (Spikevax) for COVID-19 vaccination.        No Medical History information was reported.    On an unknown date, the patient received dose of mRNA-1273 (Spikevax) (unknown route) 1 dosage form. On an unknown date, the patient experienced MULTISYSTEM INFLAMMATORY SYNDROME IN ADULTS (hyperinflammatory syndrome) (seriousness criterion medically significant), COVID-19 (breakthrough COVID-19 infection) (seriousness criterion medically significant) and HAEMOPHAGOCYTIC LYMPHOHISTIOCYTOSIS (Hemophagocytic lymphohistiocytosis) (seriousness criterion medically significant). At the time of the report, MULTISYSTEM INFLAMMATORY SYNDROME IN ADULTS (hyperinflammatory syndrome), COVID-19 (breakthrough COVID-19 infection) and HAEMOPHAGOCYTIC LYMPHOHISTIOCYTOSIS (Hemophagocytic lymphohistiocytosis) outcome was unknown.        The action taken with mRNA-1273 (Spikevax) (Unknown) was unknown.   For mRNA-1273 (Spikevax) (Unknown), the reporter considered MULTISYSTEM INFLAMMATORY SYNDROME IN ADULTS (hyperinflammatory syndrome), COVID-19 (breakthrough COVID-19 infection) and HAEMOPHAGOCYTIC LYMPHOHISTIOCYTOSIS (Hemophagocytic lymphohistiocytosis) to be related.    Company comment: This is a regulatory case concerning a 63-year-old female patient with no reported medical history, who experienced the serious (medically significant) unexpected AESI breakthrough COVID-19 infection and multisystem inflammatory síndrome in adults (MIS-A) after receiving vaccination with mRNA-1273. Details on schedule of vaccination dose number and dates were not provided. The patient exhibited clinical characteristics consistent with both MIS-A and hemophagocytic lymphohistiocytosis (HLH), as a differential diagnosis.  The benefit-risk relationship of mRNA-1273 is not affected by this report.  No concomitant and treatment medication reported  The patient exhibited clinical characteristics consistent with both multisystem inflammatory syndrome in adults (MIS-A) and hemophagocytic lymphohistiocytosis (HLH), thus posing a diagnostic challenge.  The case raises concerns regarding the lack of clear algorithms and guidelines to diagnose and manage MIS-A in adults post-COVID-19 vaccination.; Sender's Comments: Company comment: This is a regulatory case concerning a 63-year-old female patient with no reported medical history, who experienced the serious (medically significant) unexpected AESI breakthrough COVID-19 infection and multisystem inflammatory síndrome in adults (MIS-A) after receiving vaccination with mRNA-1273. Details on schedule of vaccination dose number and dates were not provided. The patient exhibited clinical characteristics consistent with both MIS-A and hemophagocytic lymphohistiocytosis (HLH), as a differential diagnosis.  The benefit-risk relationship of mRNA-1273 is not affected by this report.