¹Institute of Forensic Sciences and Legal Medicine, Istanbul University-Cerrahpasa, Istanbul, Turkiye DOI : 10.29228/jrp.544 Soon after the commencement of the mass immunization programs, the safety of the COVID-19 vaccines became a top issue. An increase is noticed in the literature in complaints and complications among the public due to a variety of adverse reactions, ranging from the most minor ones like fever, local pain, and myalgias to several potentially serious cardiac and neurological complications like blood clotting, Bell's palsy, myocarditis, hypertensive crisis, pericarditis, and other serious cardiovascular events. Transverse myelitis, cerebral venous thrombosis, and acute inflammatory demyelinating polyneuropathy were only a few among many more conditions. Most of COVID-19 vaccines function through expressing spike protein. They accomplish this either by transfecting the cells with a spike mRNA or by infecting them with an adenovirus containing a spike gene. When spike is expressed, the immune system recognizes it as a foreign antigen and mounts an attack on the protein and consequently on SARS-CoV-2 in case of any contagion. However, the spike protein is the virus's primary mechanism for infection and is accountable for the majority of the complications that COVID 19 brought. When it exists or is produced in sufficient quantities in the body, it can mimic partially a COVID-19 pathological picture, including a cytokine storm, particularly following vaccinations of infected people. In order to know the long-term safety of any new COVID-19 vaccine as any new type of pharmaceutical product, clinical data should be continuously collected for long-term adverse reactions using the country's effective pharmacovigilance systems and questioning the vaccination effect during the diagnosis in hospitals. Keywords : COVID-19 vaccine; neurological adverse reactions; side effects of mRNA vaccination; Long-term COVID-19, myocarditis, thrombosis