worsening cytopenias; worsening cytopenias; anemia; Ferritin increased; hyperferritinemia; high-grade fevers (40.1ºC); This is a spontaneous report from an unpublished manuscript via a contactable physician. A 55-year-old female patient received BNT162B2, via an unspecified route of administration on an unspecified date at single dose for COVID-19 immunisation. Medical history included GATA-2 deficiency, MDS (blasts 6-8%), MAC, pulmonary aspergillus and adult-onset Still's disease (AoSD). Concomitant medications included unspecified steroids. Patient presented with four-months of fevers, cytopenias, and hyperferritinemia. She had received steroids for presumed adult-onset Still's disease (AoSD). Her symptoms initially improved but then returned. Bone marrow culture grew MAC, and she developed pulmonary aspergillosis. Bone marrow biopsy revealed myelodysplastic syndrome (MDS) with excess blasts. She was diagnosed with GATA2 deficiency based on uniallelic GATA2 expression and was consented onto a natural history protocol at NIH (#). Her symptoms stabilized with antibiotics, but intermittent fevers persisted. She received the BNT162b2 mRNA-vaccine in preparation for chemotherapy and developed high-grade fevers (40.1 centigrade) three-days after vaccination. Ferritin increased from 2,642 to 7,724ng/mL, and she had worsening cytopenias. Due to pulmonary aspergillosis, steroids were avoided. Anakinra was trialed but not tolerated. Fevers continued but her labs stabilized over two-weeks, although she continued to need blood transfusions for anemia. Her condition then returned to baseline, and her MAC and aspergillus improved with treatment. Underlying Condition: Temperature (Celsius): 40.1; Ferritin (ng/mL): 7,724; White blood count (K/uL): 2.6; Hemoglobin (g/dL): 6.8; Platelet (K/uL): 106; Triglycerides (mg/dL): 106; Fibrinogen (mg/dL): 561; AST (U/L): 36; Organomegaly: Hepatosplenomegaly; Soluble CD25 (pg/mL): 4,907; Hemophagocytosis: ND - Not determined; H-Score: 208; EBV blood PCR (IU/mL): 1000; Treatment: Ketorolac, anakinra (not tolerated); Vaccine Response - anti-spike antibody (U/mL): Positive - 2.1. Outcome: Alive - pending chemotherapy, transplant. Outcome of the events was unknown.  The rapid generation of safe and effective mRNA vaccines has been an unprecedented success of the SARS-CoV-2 pandemic. Adverse events are extremely uncommon even in large population-database analyses. However, exacerbations of underlying hematologic and autoimmune diseases have been reported post-vaccination. Rare cases of possible vaccine-related HLH have also been reported after other SARS-CoV-2 vaccines. Given the widespread administration of these vaccines, it is essential to continue to monitor for rare adverse events and specific patient populations at-risk for them. In this case series, we describe five cases reported across the Unknown locations over the last year of hyperinflammatory reactions including HLH with temporal associations to mRNA vaccination in people with underlying immune dysregulation.  The lot number for the vaccine, BNT162B2, was not provided and will be requested during follow up.; Sender's Comments: Based on the information in the case report, a possible causal association between the events and suspect drug BNT162B2 cannot be excluded.  The impact of this report on the benefit/risk profile of the Pfizer product is evaluated as part of Pfizer procedures for safety evaluation, including the review and analysis of aggregate data for adverse events. Any safety concern identified as part of this review, as well as any appropriate action in response, will be promptly notified to regulatory authorities, Ethics Committees, and Investigators, as appropriate.