Bilateral Myositis Ossificans of the Deltoid Muscle Secondary to the COVID-19 Vaccine: A Case Report.

Shoulder injuries related to COVID-19 vaccines presented in the literature include many forms that occurred either early in the first days after injection or late, after weeks or months, but not all have convincingly demonstrated a cause-and-effect relationship. We present and illustrate a unique case to our knowledge of late-onset bilateral myositis ossificans of the deltoid muscles and spontaneous stabilization of evolution, without functional impairment of the shoulders, after the correct administration of the Pfizer-BioNTech COVID-19 mRNA vaccine. This case highlights the possibility of diagnosing some late muscle changes after this type of vaccination, which should not be considered tumor masses, and watchful waiting is recommended as a useful approach. The possibility of late side effects after vaccination has received little consideration in the past. This case report is intended to be an argument in favor of further studies to evaluate the risks, contraindications, and better management of late side effects of the new mRNA vaccines.