MG s/p COVID-19 vaccination/progressing LE weakness; This is a literature report.  A 46-year-old female patient received BNT162b2 (BNT162B2), as dose 1,  single (Batch/Lot number: unknown) for covid-19 immunisation. The patient's relevant medical history and concomitant medications were not reported. The following information was reported: MYASTHENIA GRAVIS (hospitalization, medically significant, life threatening), 5 days after the suspect product(s) administration, outcome "unknown", described as "MG s/p COVID-19 vaccination/progressing LE weakness". The patient underwent the following laboratory tests and procedures: Antibody test: negative, notes: initially; present, notes: 6 months later; Unknown results, notes: CSF studies from LP; Anti-muscle specific kinase antibody: negative; CSF test: bland basic, notes: from LP; Electromyogram: 60-70 %, notes: electrical decrement; Imaging procedure: Negative; Exam: bilateral ptosis; bilateral ptosis that improved, notes: with an ice pack test; negative; Negative; Negative; Lumbar puncture: bland basic, notes: CSF studies; negative, notes: MS; Negative, notes: AChR Ab; Nerve conduction studies: 60-70 %, notes: electrical decrement. Therapeutic measures were taken as a result of myasthenia gravis.  Additional information: INTRODUCTION: Myasthenia gravis (MG) occurs sporadically with no known causes. The authors presented a rare case of new onset MG s/p COVID-19 vaccination.   CASE PRESENTATION: A healthy 46-year-old female presented with progressing LE weakness for 3 months. Symptoms started 5 days after her initial Pfizer COVID-19 vaccine. Her workup showed negative neuroimaging, bland basic CSF studies from LP, with negative MS profile and AChR Ab. She presented again in 1 month with difficulty rising from a seated position, raising her arms above her head with blurry vision. Exam showed bilateral ptosis that improved with an ice pack test, weakness is worst in proximal muscles, but normal reflexes. Workup was again negative. Pyridostigmine was added after discharge (DC). 2 months after, she was admitted to the ICU for acute progressive fatiguability and dyspnea. EMG/NCS of the ulnar nerve showed 60-70% electrical decrement. She underwent therapeutic PLEX. Prednisone was added at DC followed by mycophenolate. 2 weeks later, she was again admitted with myasthenic crisis. She again underwent PLEX with improvement and intubation was avoided. Biweekly PLEX was started at DC. Testing for AChR, MuSK, and LRP4 Abs were initially negative, but AChRAbs were present 6 months later. She then underwent thymectomy showing hyperplasia. DISCUSSION: MG exacerbations have been attributable to infections (50%) and medications (30%). This has worsened during the COVID- 19 pandemic especially when medications such as azithromycin were used to treat acute infections. While vaccine-induced flares or onset of autoimmune diseases have been described in literatures, new onset MG following vaccines is rare, limited to 1 to 3 case reports. No case, to the authors' knowledge, correlated to the 1st dose like this patient. The temporal relationship between the COVID- 19 vaccination and onset of MG symptoms in this patient could represent a correlation, but does not prove causality. Perhaps a more plausible theory is that the vaccine may have unmasked a previously unrecognized disease in high-risk patient. The authors asked if the COVID vaccine induces a similar cytokine storm, which the immune system to a point that breaks immunologic self-tolerance. Interestingly, this patient was initially seronegative, but the presence of AChR Ab was confirmed after sensitive cell-based assays testing. This patient may have had pre-existing self-antigens to the AChR that were released after receiving the Pfizer COVID- 19 vaccine. CONCLUSION(S): The rate of COVID-19 vaccinations will soon surpass that of infections placing vulnerable individuals at risk for MG onset. Recognizing this risk will open discussions about vaccine safety. In doing so, the authors can begin to formulate new parameters for post-vaccination monitoring. The risks of and complications from acute COVID-19 still outweigh the rare adverse events from vaccines; thus, eligible patients should be offered the COVID- 19 vaccine.; Sender's Comments: Based on the current available limited information in the case provided, the causal association between the events and the use of suspect product BNT162B2 cannot be fully 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.