There are over 1000 peer-reviewed papers in the preprint server system and or in the National Library of Medicine (PUBMED) describing side effects after mRNA or adenoviral DNA COVID-19 vaccination.  One of the most dreaded complications is vaccine-induced thrombotic thrombocytopenia (VITT).  
Because the Spike protein produced in response to the vaccine genetic code causes hemagglutination and micro blood clotting, there is excessive antigenic presentation of platelets to the spleen and reticuloendothelial system.  As a result, the body produces auto-antibodies directed against a platelet receptor (PF4) which has homology with an endothelial protein.  This causes autoantibody “pinning” of platelets to the lining of blood vessel cells resulting in consumption of platelets, blood clotting and bleeding at the same time….