The patient was likely to have been suffering from vaccinia; Elevated leukocytosis of 13.4 (10E3/u); Nocturnal diaphoresis; Intermittent arthralgia; Chills; Myalgia; Tenderness was elicited at the injection site; Intermittent fever of 101 degrees Fahrenheit (38.3 degrees Celsius);   Case reference number US-BN-2023-001036 is a literature case report, title as stated above, identified on 20-Jun-2023 and concerns a 45-year-old male patient.  The aim of the article was to describe occurrence of a rare disease in an immunocompromised patient after receiving a dose of Jynneos.  A Human Immunodeficiency Virus (HIV)-positive male patient was presented to the Emergency Department (ED) with vaccinia symptoms several days after receiving the Jynneos vaccine (batch number not provided) at an unknown dose, route or site of administration for an indication reported as prophylactic administration. Given the patient's HIV status, prophylactic administration of the Modified Vaccinia Ankara (MVA) vaccine, Jynneos, was administered by the patient's primary care physician five days prior to the ED visit.   The patient presented to the ED for five days of nocturnal diaphoresis, chills, intermittent arthralgia, and myalgia. The patient reported an intermittent fever of 101 degrees Fahrenheit (38.3 degrees Celsius) but denied cough, chest pain, and dyspnea. Upon arrival to the ED, the patient was afebrile with normal vital signs. Mild tenderness was elicited at the injection site, but no erythema or swelling was appreciated. Additionally, the patient did not have signs of lymphadenopathy and was a well-appearing male in no acute distress, with all systems, including ENT, dermatologic, lymphatic, and cardiopulmonary evaluation, being grossly benign. The symptoms began several hours after the injection. Serum laboratory evaluation revealed a leukocytosis of 13.4 (×10E3/u) and elevated inflammatory markers with a C-reactive protein (CRP) of 7.0 mg/dL and an erythrocyte sedimentation rate (ESR) of 11 mm/h. Complete metabolic panel, troponin, and urinalysis were within normal limits, and the initial viral studies, corona virus disease 2019 (COVID-19) and influenza A/B antigens were negative as well. Chest X-ray did not demonstrate an acute cardiopulmonary process, and the electrocardiogram showed sinus rhythm with normal rate, interval, and axis. Given that there were no other sources of infection discovered, in conjunction with the symptoms beginning so soon after administration, the patient was likely to have been suffering from vaccinia secondary to the Jynneos vaccine. The patient was closely monitored while in the ED, and remained stable throughout the stay, endorsing a symptomatic improvement with intravenous (IV) ketorolac 30 mg and 1 liter of normal saline fluid bolus. After ensuring the patient had close and proper follow-up, the patient was provided strict return precautions and was discharged.   The patient reported complete resolution of symptoms at 14-day follow-up.  The reporter did not provide seriousness assessment for the events of 'vaccinia virus infection', 'leukocytosis', 'hyperhidrosis', 'arthralgia', 'chills', 'myalgia', 'injection site pain' and 'pyrexia', however the event 'vaccinia virus infection' was assessed as serious due to seriousness criteria of medical significance. The reporter assessed the event of 'vaccinia virus infection' as related to Jynneos vaccine, stating that the event was secondary to Jynneos vaccine, while the causality for the events of 'leukocytosis', 'hyperhidrosis', 'arthralgia', 'chills', 'myalgia', 'injection site pain' and 'pyrexia' was not provided.   No further information was provided.; Reporter's Comments: A 45-year-old male patient experienced nocturnal diaphoresis, fever, chills, intermittent arthralgia and myalgia, several hours after being vaccinated with Jynneos, dosage and route of administration not specified. Patient also had injection site tenderness. Cough, chest pain and dyspnea were denied, patient was well-appearing upon examination. No lymphadenopathy was observed. Laboratory data was remarkable for slight leukocytosis (13.4 x 10^3 cells/uL) and CRP of 7. COVID-19 and flu (A/B) tests were negative. Within 14 days, patient had recovered. The treating physicians considered vaccinia as a likely diagnosis. Vaccinia is unlisted, whereas myalgia, fever, chills, injection site pain are listed per both insert for Jynneos. Diaphoresis, arthralgia and leukocytosis are listed per summary but unlisted per insert. Patient's medical history included HIV. MVA-BN is a highly attenuated vaccine, incapable of replication, therefore cannot spread or cause vaccinia infection and disease. Distribution studies in rabbits confirmed that expression is mostly limited to the injection site. The reported adverse experiences are expected to occur with immunizations, although systemic symptoms may resemble an ongoing infection. The mild leukocyte count elevation and slight increase in CRP are consistent with the inflammatory and immunogenic response. No data was reported whether patient was tested for vaccinia (e.g. via PCR). Based on the known safety profile of Jynneos, the event of vaccinia is considered not related. The fever, chills, arthralgia, myalgia, leukocytosis, injection site pain and diaphoresis are considered related, due to the suggestive temporal relationship. Case is serious due to medical significance of the vaccinia event.; Sender's Comments: A 45-year-old male patient experienced nocturnal diaphoresis, fever, chills, intermittent arthralgia and myalgia, several hours after being vaccinated with Jynneos, dosage and route of administration not specified. Patient also had injection site tenderness. Cough, chest pain and dyspnea were denied, patient was well-appearing upon examination. No lymphadenopathy was observed. Laboratory data was remarkable for slight leukocytosis (13.4 x 10^3 cells/uL) and CRP of 7. COVID-19 and flu (A/B) tests were negative. Within 14 days, patient had recovered. The treating physicians considered vaccinia as a likely diagnosis. Vaccinia is unlisted, whereas myalgia, fever, chills, injection site pain are listed per both summary and insert for Jynneos. Diaphoresis, arthralgia and leukocytosis are listed per summary but unlisted per insert. Patient's medical history included HIV. MVA-BN is a highly attenuated vaccine, incapable of replication, therefore cannot spread or cause vaccinia infection and disease. Distribution studies in rabbits confirmed that expression is mostly limited to the injection site. The reported adverse experiences are expected to occur with immunizations, although systemic symptoms may resemble an ongoing infection. The mild leukocyte count elevation and slight increase in CRP are consistent with the inflammatory and immunogenic response. No data was reported whether patient was tested for vaccinia (e.g. via PCR). Based on the known safety profile of Jynneos, the event of vaccinia is considered not related. The fever, chills, arthralgia, myalgia, leukocytosis, injection site pain and diaphoresis are considered related, due to the suggestive temporal relationship. Case is serious due to medical significance of the vaccinia event.