left bundle branch block; lethargy; loss of energy; bicep pain specific to the bicep tendon and antecubital fossa which comes and goes; he had a couple of tick bites; feeling like he could sleep all day; fatigue; muscle pain/muscle aches/bicep pain specific to the bicep tendon and antecubital fossa which comes and goes; This spontaneous case was reported by a patient and describes the occurrence of BUNDLE BRANCH BLOCK LEFT (left bundle branch block) in an 84-year-old male patient who received mRNA-1273.815 (SPIKEVAX 2023-2024) for COVID-19 prophylaxis. The occurrence of additional non-serious events is detailed below.     Concurrent medical conditions included Type 2 diabetes mellitus.    On an unknown date, the patient received third dose of mRNA-1273.815 (SPIKEVAX 2023-2024) (unknown route) 1 dosage form. On an unknown date, the patient experienced BUNDLE BRANCH BLOCK LEFT (left bundle branch block) (seriousness criterion life threatening), LETHARGY (lethargy), ASTHENIA (loss of energy), PAIN IN EXTREMITY (bicep pain specific to the bicep tendon and antecubital fossa which comes and goes), ARTHROPOD BITE (he had a couple of tick bites), SOMNOLENCE (feeling like he could sleep all day), FATIGUE (fatigue) and MYALGIA (muscle pain/muscle aches/bicep pain specific to the bicep tendon and antecubital fossa which comes and goes). The patient was treated with AMOXICILLIN SODIUM, CLAVULANATE POTASSIUM (AUGMENTIN [AMOXICILLIN SODIUM;CLAVULANATE POTASSIUM]) at an unspecified dose and frequency and DOXYCYCLINE at an unspecified dose and frequency. At the time of the report, BUNDLE BRANCH BLOCK LEFT (left bundle branch block), LETHARGY (lethargy), ASTHENIA (loss of energy), PAIN IN EXTREMITY (bicep pain specific to the bicep tendon and antecubital fossa which comes and goes), FATIGUE (fatigue) and MYALGIA (muscle pain/muscle aches/bicep pain specific to the bicep tendon and antecubital fossa which comes and goes) had not resolved and ARTHROPOD BITE (he had a couple of tick bites) and SOMNOLENCE (feeling like he could sleep all day) outcome was unknown.        For mRNA-1273.815 (SPIKEVAX 2023-2024) (Unknown), the reporter did not provide any causality assessments.   The patient did not receive any other vaccines in the 4 weeks prior to COVID-19 vaccine. No concomitant medication was reported. The patient took the first 2 immunizations of Moderna followed by an additional booster dose. The patient was not sure which presentation of the Moderna vaccines was given for on 3rd dose. The patient began to fell lethargy, a loss of energy, muscle pain, muscle aches, and a feeling like the patient could sleep all day. The patient had also had some bicep pain specific to the bicep tendon and antecubital fossa which comes and goes. This was acute intermittent pain. The patient also experienced a left bundle branch block around this time. The patient had not performed any new weightlifting activities and previously was very active prior to these symptoms starting. The patient also noted around when these symptoms started the patient had a couple of tick bites. The patient took Augmentin and Doxycycline for these. The patient continues to have this fatigue and bicep pain symptoms today  Company Comment: This is a Spontaneous case concerning a 84-year-old male patient with concurrent type 2 diabetes, who experienced the serious (per Life threatening) unexpected event of Bundle branch block left which occurred on an unknown onset latency with a dose of mRNA-1273.815 received as the third dose for COVID-19 Vaccination. Patient's advanced age and type 2 diabetes could remain confounding cardiovascular risk factors. He reported experiencing lethargy, a loss of energy, muscle pain, muscle aches, and somnolence. The patient also reported to suffered tick bites when the symptoms started which could also remain a confounder. Treatment with Augmentin and Doxycycline was reported. The event had not resolved. The benefit-risk relationship of mRNA-1273 is not affected by this report.