This case was reported in a literature article and described the occurrence of neuromyelitis optica spectrum disorder in a adult subject who received Flu vaccine unspecified for prophylaxis. The subject's past medical history included neuromyelitis optica spectrum disorder. On an unknown date, 32 days after receiving Flu vaccine unspecified, the subject developed neuromyelitis optica spectrum disorder. Serious criteria included GSK medically significant. Additional event(s) included myelitis with serious criteria of GSK medically significant. The outcome of neuromyelitis optica spectrum disorder was recovered/resolved. The outcome(s) of the additional event(s) included myelitis (recovered/resolved). The investigator considered that there was a reasonable possibility that the neuromyelitis optica spectrum disorder and myelitis may have been caused by Flu vaccine unspecified. Relevant Tests: Lab tests were performed on unspecified date. Expanded Disability Status Scale (EDSS) from baseline to nadir was 2.5. AQP-4 serostatus was positive. Additional information was provided. This case was reported in a literature article and described the relapse of neuromyelitis optica spectrum disorder (NMOSD) and myelitis in a patient aged 38.4 and 60-year of unspecified gender who was vaccinated with unspecified inactivated influenza vaccine (manufacturer unknown) for prophylaxis. The patient was a part of retrospective analysis that investigated the association of a relapse occurring within 30, 60, and 90 days of a vaccination and compared it with the association of a relapse occurring within randomly selected dates. The goal was to determine if vaccines may increase the risk of a Neuromyelitis optica spectrum disorder (NMOSD) relapse conducted at three NMOSD centers world-wide. The patient had a history of NMOSD. The patient was not on immunotherapy at the time of vaccination. No information on patient's family or medical history or concurrent condition or concomitant medication was provided. On 15 October 2014, the patient received unspecified inactivated influenza vaccine intramuscularly (administration site unspecified; dosages unknown; batch number not provided). Age of vaccination was not provided. On an unspecified date, 32 days after vaccination, the patient had a relapse of NMOSD and myelitis. [In this study, relapses were defined across all centers as a new or worsening acute neurologic symptom lasting at least 24h, associated with a change in exam localizing to the central nervous system (CNS) and not explainable by fever, infection or metabolic condition. Magnetic resonance imaging (MRI) was used for relapse confirmation as needed. Relapse severity was characterized by net change in the Expanded Disability Status Scale (EDSS) from baseline to nadir]. EDSS from baseline to nadir was 2.5. AQP-4 serostatus was positive. In this study, the duration of disease was 3.1 and 10.8 years. Treatment was unknown. The outcome of the event was not reported. The author considered the event of relapse of NMOSD and myelitis temporally associated with unspecified influenza vaccine. The author concluded, "comprehensive, well-controlled prospective analysis that assesses relapses, vaccines and infections would be warranted for future research to confirm our findings that suggest that patients who are treated with preventive immune suppression and receive routine vaccinations for common infections may fare better than those who do not." This is 1 of 13 valid cases reported in the same literature article. Lab Comments: Lab tests were performed on unspecified date. Expanded Disability Status Scale (EDSS) from baseline to nadir was 2.5. AQP-4 serostatus was positive.