Guillain-Barre syndrome/acute inflammatory demyelinating polyneuropathy; Chronic inflammatory demyelinating polyneuropathy; weakness in his legs; numbness in his legs; This case was reported in a literature article and described the occurrence of guillain barre syndrome in a elderly male patient who received Flu unspecified (Influenza vaccine) for prophylaxis. (Guillain-Barre syndrome, or acute on chronic inflammatory demyelinating polyneuropathy, following Moderna Covid-19 vaccine.)  The patient's past medical history included coronary artery disease (requiring coronary artery bypass graft, coronary artery stents) and sick sinus syndrome (require dual-chamber pacemaker).   On an unknown date, the patient received Influenza vaccine. On an unknown date, immediately after receiving Influenza vaccine, the patient experienced guillain barre syndrome (serious criteria GSK medically significant), chronic inflammatory demyelinating polyneuropathy (serious criteria GSK medically significant), lower extremities weakness of and numbness in leg. The patient was treated with operations and procedures (Plasma Exchange) and operations and procedures (Plasmapheresis (Nos)). On an unknown date, the outcome of the guillain barre syndrome and chronic inflammatory demyelinating polyneuropathy were recovering/resolving and the outcome of the lower extremities weakness of and numbness in leg were not recovered/not resolved.   It was unknown if the reporter considered the guillain barre syndrome, chronic inflammatory demyelinating polyneuropathy, lower extremities weakness of and numbness in leg to be related to Influenza vaccine.  Additional information was reported as follows: This case was reported in a literature article and described the occurrence of Guillain-Barre syndrome (GBS) in a male patient aged between 83 to 87-year old, who was vaccinated with unspecified influenza vaccine (manufacturer unknown) for prophylaxis. The patient had medical history of coronary artery disease requiring coronary artery bypass graft, coronary artery stents, and a dual-chamber pacemaker for sick sinus syndrome. No information on patient's family history, concurrent condition or concomitant medication was provided. On an unspecified date, the patient received unspecified influenza vaccine (administration route and site unspecified, dosage unknown; batch number not provided). The age of vaccination was not provided. On an unspecified date in 2017, shortly after receiving the vaccination, the patient had symptoms, laboratory, and electrophysiological features of Guillain-Barre syndrome (GBS)/acute inflammatory demyelinating polyneuropathy (AIDP). Thyroid function tests, hemoglobin A1c, serum protein electrophoresis, syphilis and Lyme titers were unremarkable. The patient had incomplete resolution of symptoms with a course of five plasma exchange treatments. One month after initial diagnosis and treatment, it was determined that the patient's condition had evolved to chronic inflammatory demyelinating polyneuropathy (CIDP), for which the patient received ongoing plasmapheresis on an every two week basis, with symptom improvement but not normalization. [At the time of reporting, the patient was 87 year old and presented with acute worsening weakness and paresthesia of bilateral lower extremities. In March 2021, the patient had onset over twelve hours of significantly worse weakness and numbness in his legs, similar to his prior AIDP/GBS. It was noted that the patient had received a Moderna COVID-19 vaccine twenty-one days prior. His physical exam was notable for normal strength in the upper extremities, with diminished but present reflexes. Lower extremity exam revealed bilateral weakness in the hip, distal extremities, and feet. Ankle and knee reflexes were absent. Cerebrospinal fluid contained elevated protein. Electromyography revealed F-waves in the lower extremities. The patient was treated with a more intensive course of plasmapheresis consisting four treatments over ten days. His strength and sensation improved to baseline over this period]. The authors commented, "We describe a patient with a history of AIDP/GBS, evolving into CIDP, who developed exacerbated CIDP (or AIDP) coinciding with receipt of the Moderna COVID-19 vaccine." The authors concluded, "GBS/AIDP, or exacerbation of CIDP, is herein described to have coincided with the recent Moderna COVID-19 vaccine. More studies are needed to determine whether our patient's clinical deterioration was merely coincident with receipt of vaccine or whether a cause-and-effect relationship exists."