This report was received with assigned Manufacturer Control Number of 22-0004-05058. Case Description: Follow up information received on 15 Apr 2022 included laboratory results. Case Number 22-0004-05058 is an investigator report of Chest Pain in a 34-year-old male subject enrolled in Unknown protocol. The local Monitor has assessed the event as serious, expected and related to the study product. The subject's past medical history included attention deficit hyperactivity disorder (ADHD), scoliosis and seasonal allergies. He is allergic to Benadryl (diphenhydramine) (reaction not provided). Concomitant medication included multivitamin from 2010 for general health. On 16 April 2021, the subject received the first dose of the Pfizer mRNA BNT162b2 vaccine, 30 mcg for coronavirus disease 2019 (COVID-19) prophylaxis. On 07 May 2021, the subject received the second dose of the Pfizer mRNA BNT162b2 vaccine, 30 mcg. On 12 November 2021, the subject received the third dose of the Pfizer mRNA BNT162b2 vaccine, 30 mcg. On 04 April 2022, the subject was enrolled and randomized to study arm 1. He received the first and only dose of the study product mRNA-1273 Prototype, 50 mcg administered intramuscularly (IM). Reactogenicity records were not provided. The subject received the last dose of the study product prior to the onset of the serious adverse event (SAE) on this day. On 05 April 2022 and 06 April 2022, the subject noted myalgia, fatigue and "maybe chest discomfort but unclear". This was consistent with prior reactogenicity symptoms from previous mRNA vaccinations. On 07 April 2022, the subject's symptoms resolved except for slight chest discomfort without dyspnea or other symptoms. He took two doses of ibuprofen 200 mg. On 08 April 2022, the subject's chest discomfort persisted. He called the clinic and was seen that afternoon. Per the site, the subject's chest discomfort improved while lying flat and worsened a little while sitting up and leaning forward. He experienced no limitation or difficulty with activities such as "walking miles" or with stairs at his home. His vital signs (VS) included a temperature of 37 degrees Celsius, blood pressure (BP) of 109/71 mmHg and heart rate of 73 beats per minute (bpm). The subject's physical examination showed him appearing well, clear lungs, extremities "benign", slight tenderness to palpation over the left lower sternal border at the 6th to 8th costochondral junction and no murmurs, rubs or gallops. An electrocardiogram (EKG) showed an incomplete right bundle branch block (RBBB) but was otherwise unremarkable. Laboratory results included an elevated troponin-T of 18 ng/L (Normal Range [NR]: 0-14), troponin-I of <0.01 ng/mL (NR: 0.00-0.03) and creatine kinase myocardial band (CK-MB) of 2.5 ng/mL (NR: 0.0-7.7). On 09 April 2022, the subject felt better but his chest discomfort persisted. On 10 April 2022, the subject was evaluated in the clinic. His physical examination showed clear lungs, cardiac exam within normal limits (WNL) with no murmurs, rubs or gallops, extremities "benign", no left chest wall discomfort and slight tenderness to palpation over the right lower sternal border at the costochondral junction. Cardiac magnetic resonance imaging (MRI) was performed and showed no evidence of pericarditis or myocarditis, and normal biventricular size and systolic function. On 11 April 2022, the subject was seen again in the clinic. His VS showed a temperature of 37 degrees Celsius, BP of 112/70 mmHg and heart rate of 83 bpm. The subject's physical exam showed him looking well, and persistent and very slight discomfort over his right lower sternal border with palpation. His physical examination was otherwise normal. An EKG was repeated and unchanged from his EKG on 08 April 2022 and showed incomplete RBBB but was otherwise unremarkable. Laboratory results included a troponin-T of 16 ng/L. Per the site, it was assessed that the subject had a troponin leak post vaccination. There was no evidence for myocarditis given the clinical findings and overall laboratory testing. The event, Chest Pain, was considered recovering/resolving. Per the Investigator (PI), the event was related to the study product. Assessment: The Investigator has assessed the event, Chest Pain, as serious (Important medical event) and related to the study product. Follow Up Required: Yes. The following information will be requested: 1. Please provide the reactogenicity records for the subject. 2. Please provide the final outcome and resolution date when available, and update Section 4 of form accordingly. Company Comment: This case concerns a 34 year-old, male subject with a history of attention deficit hyperactivity disorder (ADHD), scoliosis and seasonal allergies, who experienced the expected event of chest pain. The event occurred approximately 2 days after the last dose of mRNA-1273. The event was assessed as related to study drug in agreement with the Investigator. Reporter's Comments: Company Comment: This case concerns a 34 year-old, male subject with a history of attention deficit hyperactivity disorder (ADHD), scoliosis and seasonal allergies, who experienced the expected event of chest pain. The event occurred approximately 2 days after the last dose of mRNA-1273. The event was assessed as related to study drug in agreement with the Investigator.