Probably had an aneurysm/aortic aneurysm/35 cm dissecting aneurysm of interior layer; Pain in left arm and back; Lost function in right leg/not able to move right leg at this point/still was not able to move leg/problems with right leg; Get the swelling down/swelling in his leg; Pain in left arm and back; Tingling in left arm and back; Having a reaction; Using a walker; Lost 25 pounds of muscle; This spontaneous case was received on 04-Nov-2020 from other non-health professional (consumer) via Med Communications (reference number: SEQW20-04775) and concerned a 64-year-old, male patient.  The patient's concurrent conditions included mild cholesterol elevation started six months ago. It was reported that the patient was a jogger of four to five miles per day. The patient's concomitant medication included Vytorin (ezetimibe, simvastatin) used for an unreported indication.  On 14-Sep-2020, the patient was vaccinated with Flucelvax QIV (influenza vaccine, subunit influenza virus vaccine polyvalent; dose: 0.5 ml, anatomical location: left deltoid, route of administration: not reported) as influenza prophylaxis. The batch number reported was 279840 and expiry date reported was Jun-2021.  On the same day, within 15 minutes after receiving Flucelvax QIV, the patient went back to his office and noticed tingling and pain in his left arm and back. The patient went back to the clinic area and told the person that administered the vaccine that he thought he was having a reaction. The patient was not able to move his leg at that point. The 911 was called and the patient was taken to hospital and they initially thought that he was having a stroke, however, the emergency room (ER) doctor said he probably had an aneurysm. A computerized tomography (CT) scan was performed and revealed an aortic aneurysm. The patient was airlifted to hospital where a team was waiting on him and he was immediately taken to the surgery. The patient had a 35 cm dissecting aneurysm of interior layer and two stents were placed. The surgery lasted two and a half hours. The patient was still not able to move his leg.   At the hospital, they worked to get the swelling down and control the patient's blood pressure. It was reported that the patient had no blood pressure problems until this happened, and that he was jogging that morning before going to work. The assessment was that the swelling in the patient's leg was affecting lumbar plexus that caused problems with right leg.  On 26-Sep-2020, the patient was discharged from the hospital.  On an unspecified date, the patient lost 25 pounds of muscle and was trying to rebuild muscle. The patient was using a walker.   At the time of initial reporting on 04-Nov-2020, the patient had not recovered from the events.  The reporter did not provide causality assessment.  The events of 'walker user' and 'muscle wasting' were assessed as serious due to criteria of medically significant, while all other events were assessed as serious due to hospitalisation.  Company comment: The patient experienced aortic dissection, back pain, musculoskeletal stiffness, muscle atrophy, walking aid user, peripheral swelling, pain in extremity, paraesthesia and unspecified adverse reaction after administration of Flucelvax QIV. Reportedly, 15 min post vaccination the events slowly started to appear - firstly in the patient left arm and back. After that he was not able to move his leg which was followed by swelling of the leg and in the end dissecting aneurysm was established followed by surgical intervention. After surgery the patient complained how he couldn't move his leg and report of loss of muscle mass was noted. On 26-Sep-2020, the patient was discharged from the hospital, presumably in good health condition. Causality is assessed as not related for all events (can be explained with reported aneurism and jogging) except for pain in extremity, back pain and paraesthesia (assessed as possibly related due to temporal, biological and anatomical plausibility - vaccine was given in left deltoid. Unspecified adverse reaction is unassessable.; Sender's Comments: The patient experienced aortic dissection, back pain, musculoskeletal stiffness, muscle atrophy, walking aid user, peripheral swelling, pain in extremity, paraesthesia and unspecified adverse reaction after administration of Flucelvax QIV. Reportedly, 15 min post vaccination the events slowly started to appear - firstly in the patient left arm and back. After that he was not able to move his leg which was followed by swelling of the leg and in the end dissecting aneurysm was established followed by surgical intervention. After surgery the patient complained how he couldn't move his leg and report of loss of muscle mass was noted. On 26-Sep-2020, the patient was discharged from the hospital, presumably in good health condition. Causality is assessed as not related for all events (can be explained with reported aneurism and jogging) except for pain in extremity, back pain and paraesthesia (assessed as possibly related due to temporal, biological and anatomical plausibility - vaccine was given in left deltoid. Unspecified adverse reaction is unassessable.