Patient experienced seizure like symptoms; May have some SOB but not as bad; Carbon dioxide came back little high; Increase in generalized weakness and SOB on exertion; Muscle twitches; Increase in generalized weakness; Experienced a worsening of her gMG symptoms; This spontaneous case was reported by a consumer and describes the occurrence of MYASTHENIA GRAVIS (Experienced a worsening of her gMG symptoms) and SEIZURE LIKE PHENOMENA (Patient experienced seizure like symptoms) in an adult female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.    Co-suspect product included non-company product ECULIZUMAB (SOLIRIS) for Myasthenia gravis.    Concurrent medical conditions included Myasthenia gravis.   On an unknown date, the patient received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form and ECULIZUMAB (SOLIRIS) (unknown route) 1 dosage form. On 01-Feb-2021, the patient experienced MYASTHENIA GRAVIS (Experienced a worsening of her gMG symptoms) (seriousness criterion medically significant). On an unknown date, the patient experienced SEIZURE LIKE PHENOMENA (Patient experienced seizure like symptoms) (seriousness criterion medically significant), DYSPNOEA (May have some SOB but not as bad), HYPERCAPNIA (Carbon dioxide came back little high), DYSPNOEA EXERTIONAL (Increase in generalized weakness and SOB on exertion), MUSCLE TWITCHING (Muscle twitches) and ASTHENIA (Increase in generalized weakness). At the time of the report, MYASTHENIA GRAVIS (Experienced a worsening of her gMG symptoms), SEIZURE LIKE PHENOMENA (Patient experienced seizure like symptoms), DYSPNOEA EXERTIONAL (Increase in generalized weakness and SOB on exertion) and ASTHENIA (Increase in generalized weakness) was resolving, DYSPNOEA (May have some SOB but not as bad) and HYPERCAPNIA (Carbon dioxide came back little high) had not resolved and MUSCLE TWITCHING (Muscle twitches) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On an unknown date, Blood test: high (High) Carbon dioxide came back a little high.. On an unknown date, Carbon dioxide: 33 or 34 (High) 33 or 34, Carbon dioxide was little high..         Concomitant medications, vaccination history, and the patient's allergies were not reported. Patient had initiated treatment with Eculizumab (Soliris) on an unspecified date but prior to COVID Moderna vaccine. Patient got the events post the second dose. Patient reported Eculizumab to help her not have seizure-like problems.The most recent dose of eculizumab administered prior to the onset of the events was not reported. Eculizumab batch number and the expiry date were unknown. Her symptoms of Myasthenia gravis, generalized weakness and SOB on exertion improved gradually over a month. The patient had some blood work done and her carbon dioxide came back a little high which happened before, and the patient thinks because of that her muscles twitches. The patient talked to her doctor friend and he said that her body twitches at night too so, that could be why she feels it in the mornings also. Action taken with eculizumab in response to the events was not reported. Treatment for the events was not reported. The reporter causality assessment between the events and eculizumab was not reported.   Company comment: This spontaneous case concerns an adult female patient, with no medical history reported, who experienced the unexpected serious events of myasthenia gravis (described as worsening of gMG symptoms) and seizure like phenomena, considered as medically significant, along with non serious events of dyspnoea, hypercapnia, dyspnoea exertional, asthenia and muscle twitching. The events occurred after the second dose of mRNA-1273. Date of second dose administration was not provided. As reported, following her second dose of the Moderna COVID-19 vaccine, the patient experienced a worsening of her gMG symptoms. Patient also experienced an increase in generalized weakness and SOB on exertion. The patient experienced seizure-like problems, as reported. The patient had some blood work done and her carbon dioxide came back a little high which happened before, and the patient thought  because of that she had muscles twitches. Patient's symptoms improved gradually over a month as reported. However, it was also stated that patient still had SOB. Co-suspect Eculizumab remains as confounder. Although patient's medical history was not reported it is likely that patient had underlying myasthenia and experienced worsening of symptoms which likely contributed to the rest of the events above mentioned. Seizure like phenomena could have been caused by hypercapnia. The benefit-risk relationship of mRNA-1273 is not affected by this report.; Sender's Comments: This spontaneous case concerns an adult female patient, with no medical history reported, who experienced the unexpected serious events of myasthenia gravis (described as worsening of gMG symptoms) and seizure like phenomena, considered as medically significant, along with non serious events of dyspnoea, hypercapnia, dyspnoea exertional, asthenia and muscle twitching. The events occurred after the second dose of mRNA-1273. Date of second dose administration was not provided. As reported, following her second dose of the Moderna COVID-19 vaccine, the patient experienced a worsening of her gMG symptoms. Patient also experienced an increase in generalized weakness and SOB on exertion. The patient experienced seizure-like problems, as reported. The patient had some blood work done and her carbon dioxide came back a little high which happened before, and the patient thought  because of that she had muscles twitches. Patient's symptoms improved gradually over a month as reported. However, it was also stated that patient still had SOB. Co-suspect Eculizumab remains as confounder. Although patient's medical history was not reported it is likely that patient had underlying myasthenia and experienced worsening of symptoms which likely contributed to the rest of the events above mentioned. Seizure like phenomena could have been caused by hypercapnia. The benefit-risk relationship of mRNA-1273 is not affected by this report.