THYMOMA; AUTOIMMUNE ENCEPHALITIS; This spontaneous report was received from literature: This report concerned a 47-year-old male of unspecified race and ethnicity. The objective of this study was to discuss a case of thymoma-associated autoimmune encephalitis (TAAE) induced by covid-19 booster vaccine. The patient's height, and weight were not reported. The patient's pre-existing medical conditions included: Patient had no past medical history. The patient previously received covid-19 vaccine ad26. cov2. s (Dose number in series 1) (suspension for injection, route of admin, and batch number were not reported, expiry: unknown) dose was not reported, 01 total administered on an unspecified date for covid-19 prophylaxis.  It was unknown whether patient had any adverse events following the vaccination with first dose of covid-19 vaccine ad26. cov2. s (Dose number in series 1).  The patient received covid-19 vaccine ad26.cov2.s (Dose number in series 2) (suspension for injection, route of admin, and batch number were not reported, expiry: unknown) dose was not reported, 01 total administered on an unspecified date for covid-19 prophylaxis. The batch number was not reported. Per procedure, no follow-up will be requested for this case. No concomitant medications were reported. On an unspecified date (3 days after a Johnson and Johnson coronavirus-2019 (COVID-19) booster vaccine), patient was presented with worsening acute altered mental status over the past week (Dose number in series 2). Patient complained of episodes of fever and chills prior to this. Patient also had abrupt changes in memory, personality and meningitis (coded to thymoma and  autoimmune encephalitis (Dose number in series 2). On an unspecified date, the patient was hospitalized. Upon admission, the patient had a glasgow coma scale of 4. The patient was intubated and transferred to the intensive care unit. Patient was treated with intravenous (IV) vancomycin, ceftriaxone and acyclovir was for meningitis. Laboratory data (dates unspecified) included: Computed tomography (CT) scan of the head without contrast was unremarkable. Magnetic resonance imaging (MRI) showed enhancements of the right anterior and medial temporal lobe suggesting encephalitis. Cerebrospinal fluid analysis (CSF) revealed lymphocytic pleocytosis. A CT scan of the chest, abdomen and pelvis showed an anterior mediastinal mass measured 1.8 x 2.3 cm. Filmarray meningitis polymerase chain reaction as well as herpes simplex virus (HSV) 1 and 2 was negative. Autoimmune encephalitis antibody was positive for Anti-AMPAR (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor). Patient had given pulse dose steroids and intravenous immunoglobulin but failed, rituximab was initiated and cardiothoracic surgery completed a thymectomy. The number of days of hospitalization was not reported.  The action taken with covid-19 vaccine ad26.cov2.s was not applicable. The outcome of the thymoma and autoimmune encephalitis was not reported. The Authors discussed, this patient was free of symptoms prior to the COVID-19 vaccine booster, and demonstrated altered mental status hours after receiving it. This furthers the possibility of an association of the COVID-19 booster vaccine, development of encephalitis, and in this case a thymoma. Despite this, conclusions can not be made on the account of one report, but introduces a new area of focus to study.  This report was serious (Hospitalization Caused / Prolonged, and Life Threatening).; Sender's Comments: V0- 20221030387-covid-19 vaccine ad26.cov2.s-Thymoma.The event(s) shows an incompatible temporal relationship. Therefore, this event(s) is considered not related. V0- 20221030387-covid-19 vaccine ad26.cov2.s- Autoimmune encephalitis- The case causality is considered NOT RELATED. (The event of Autoimmune encephalitis is confounded by the concurrent event of Thymoma, hence considered as not related)