Abstract Background Vaccination is one of the most important ways to prevent infection or reduce incision. Vaccines manufactured in new, modified ways such as an mRNA-type and encoding the Spike protein vaccine can cause several medical problems, including blood clotting. This study aims to estimate some of the clotting factors in the blood. Methods: The 100 samples were divided into two groups: a healthy individual group before vaccination and another group after vaccination with the (Pfizer-BioNTech) vaccine for both genders. Protein C (PTN-C), protein S (PTN-S), prothrombin time (PT), partial thromboplastin time (PTT), international normalized ratio (INR), total calcium (Ca tot), albumin (Alb.) were all determined and calculated calcium ionized (Ca2+) total calcium-corrected (corr. Ca tot) and calcium ionized-corrected (corr. Ca2+). Results: The result is shown for PTN-S, PT, INR, Ca, Ca2+, corr.Ca and corr. Ca2+ a highly significant increase in unvaccinated compared to vaccinated people .While the Alb. gave a highly significant decrease. At the same time, there was no significant difference for both PTN-C and PTT between these studied groups. Conclusions: According to the study's findings, Pfizer BioNTech vaccination induces the occurrence of a clot is possible for those who have factors that contribute to the occurrence of a clot.

Keywords: Protein C, Protein S, Prothrombin Time, Thromboplastin Time, International normalized ratio.