BACKGROUND The COVID-19 pandemic is a current global crisis, and there are hundreds of millions of individuals being vaccinated worldwide. At present, there have been few reports of COVID-19 vaccine-induced autoimmune processes manifested as myositis, thrombocytopenia, and myocarditis. CASE REPORT A 37-year-old man presented to the Emergency Department (ED) with a 3-day history of back pain and a 1-day history of left upper limb swelling with paresthesia and shortness of breath, 12-days after receiving the first dose of Pfizer/BioNTech BNT162b2 mRNA COVID-19 vaccine. He was diagnosed with severe myositis complicated with rhabdomyolysis and non-oliguric acute kidney injury, thrombocytopenia, myocarditis with pulmonary edema, and pulmonary hemorrhage. Screens for potential toxic, infectious, paraneoplastic, and autoimmune disorders were unremarkable. The patient was treated with a 5-day course of intravenous methylprednisolone and intravenous immunoglobulin, with a good response. He was hospitalized for 16 days and discharged home on a tapering dose of oral prednisolone for 6 weeks. CONCLUSIONS The case describes a possible link between Pfizer/BioNTech BNT162b2 mRNA COVID-19 vaccine and immune-mediated myocarditis, pulmonary vasculitis, myositis, and thrombocytopenia. However, further data are required to confirm such an association.