MYELINIC FORM OF POST-VACCINAL ACUTE DISSEMINATED ENCEPHALOMYELITIS (ADEM); This spontaneous report received from a patient via social media via a company representative concerned an adult male of unspecified age, race and ethnicity. The patient's height, and weight were not reported. No past medical history or concurrent conditions were reported. The patient received covid-19 vaccine ad26.cov2.s (suspension for injection, route of administration not reported) on 13-JUL-2021 for prophylactic vaccination. The batch number was not reported. Per procedure, no follow-up will be requested for this case. No concomitant medications were reported.  On 25-JUL-2021, 12 days after his vaccination, the patient started feeling a tingling and numbness in his left foot. This quickly progressed up his left leg and then started on his right foot and travelled up his right leg. Within two hours, the patient could not walk or stand and was hospitalized (dates unspecified). The neurologist was concerned that the patient had developed a myelinic form of Post-Vaccinal Acute Disseminated Encephalomyelitis (ADEM). The patient had swelling on his spine at the T7  T8 area of his back which was producing the paralysis. On an unspecified date, the patient was treated with two rounds of steroids and intravenous immunoglobulin (IVIg) therapy, some swelling had gone down and it was reported that, patient's mobility had not returned at the time of report. The number of days of hospitalization was not reported and it was unsure if the patient discharged from the hospital.  The action taken with covid-19 vaccine ad26.cov2.s was not applicable. The patient had not recovered from myelinic form of post-vaccinal acute disseminated encephalomyelitis (adem). This report was serious (Hospitalization Caused / Prolonged).  Additional information received on 08-JUN-2022. The following information was updated and incorporated into case narrative: additional reporter added (company representative). Upon review, the following information was amended: Case validity changed to valid, as it was received from a company managed social media account. Event outcome updated to not recovered/not resolved in the seriousness criteria tab.; Sender's Comments: V2 Additional information in this version updates of additional reporter added (company representative). Upon review, the following information was amended: Case validity changed to valid, as it was received from a company managed social media account. Event outcome updated to not recovered/not resolved in the seriousness criteria tab. This updated information does not change the prior causality assessment of reported event. This spontaneous report received from a patient via social media concerned an adult male of unspecified age, race and ethnicity who was hospitalized for myelinic form of Post-Vaccinal Acute Disseminated Encephalomyelitis (ADEM) 12 days post vaccination. No past medical history, concurrent conditions and concomitant medications were reported.  12 days post vaccination the patient started feeling  tingling and numbness in his left foot. This quickly progressed up his left leg and then started on his right foot and travelled up his right leg. Within two hours, the patient could not walk or stand and was hospitalized. The neurologist was concerned that the patient had developed a myelinic form of Post-Vaccinal Acute Disseminated Encephalomyelitis (ADEM). The patient had swelling on his spine at the T7  T8 area of his back which was producing the paralysis. On an unspecified date, the patient was treated with two rounds of steroids and IVIG therapy. Patient's mobility had not returned at the time of report and has not recovered from the events. Information is limited in this case, and the occurrence of the events could represent background incidence of such events in the general population. However, a relationship with Janssen Covid-19 vaccine cannot be ruled out and thus the relationship is considered indeterminate.