ACUTE-ONSET CHRONIC INFLAMMATORY DEMYELINATING POLYRADICULONEUROPATHY; GUILLAIN-BARRE SYNDROME; This spontaneous report was received from literature. This report concerned a 67 year old male of an unspecified race and ethnicity. The objective of the authors was to present the first case of acute-onset chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) after Ad26.COV2.S (johnson and johnson) vaccination. The patient's weight, height, and medical history were not reported. The patient received covid-19 vaccine ad26.cov2.s (suspension for injection, route of admin, batch number and expiry date were not reported) dose, start therapy date were not reported, 1 total administered for covid-19 prophylaxis. Age at time of vaccination 7 decade old. The batch number was not reported. Per procedure, no follow-up will be requested for this case. No concomitant medications were reported.  It was reported in the article that patient presented with one-week history of progressive left facial droop, unsteady gait, slurred speech, double vision, and patchy numbness. Patient reported Ad26.COV2.S vaccination three weeks before presentation. On initial examination, he had left facial palsy, partial left abducens nerve palsy, generalized areflexia, severe lower extremities ataxia, and diminished vibratory sensation in toes. Cerebrospinal fluid analysis showed albuminocytologic dissociation. He received intravenous immunoglobulin (IVIG) for five days for presumptive diagnosis of Guillain-Barre syndrome (GBS). Electrodiagnostic studies demonstrated impersistent F-waves, decreased recruitment in lower extremities, and bilaterally absent blink reflexes. He developed right facial weakness on day three of treatment and asymmetric appendicular muscle weakness on day five of treatment. Seven weeks after symptom onset, his lower extremities weakness worsened, and received a second cycle of IVIG. The lower extremity weakness did not improve but remained stable until seventeen weeks after symptom onset when he returned with progressive upper extremities weakness and dyspnea. Electrodiagnostic studies demonstrated demyelinating features consistent with CIDP. Neuromuscular ultrasound demonstrated multifocal median nerve enlargements at non-entrapment sites. At that point, given the clinical course, electrodiagnostic and ultrasonographical findings, chronic inflammatory demyelinating polyradiculoneuropathy diagnosis (acute-onset CIDP) was established. The action taken with covid-19 vaccine ad26.cov2.s was not applicable. The patient had not recovered from acute-onset chronic inflammatory demyelinating polyradiculoneuropathy, and Guillain-barre syndrome. The authors concluded that this patient's acute-onset CIDP and other reported GBS cases after adenoviral vector COVID-19 vaccinations shared similar and atypical presenting symptoms, which were not seen in GBS after mRNA COVID-19 vaccinations. While a causal relationship cannot be established to his COVID-19 vaccination, this case adds to the evolving literature of COVID19 vaccination-associated neurological events. This report was serious (Other Medically Important Condition).; Sender's Comments: V0: 20230717242- acute-onset chronic inflammatory demyelinating polyradiculoneuropathy. The event has a compatible/suggestive temporal relationship, is unlabeled, and is scientifically plausible. There is no information on any other factors potentially associated with the event. Therefore, this event is considered consistent with vaccine administration. 20230717242-Guillain-Barre syndrome. The event has a compatible/suggestive temporal relationship, and is labeled. There is no information on any other factors potentially associated with the event. Therefore, this event is considered consistent with vaccine administration.