Abstract: COVID.19 represent the biggest disaster faced human community from last years and up to the date, despite of huge effort exerted to give therapeutic or immunization protocols, most of these attempts facing unexpected health disorders resulted as outcomes of its implication. Certain types of COVID.19 vaccines, reported to cause thrombosis in rare condition, certainly among women in puberty period, hypothesis of using factor XI as one of the components of these types of immunization, beside high level of sex hormones, particularly estradiol, which is usually accompanied with high levels of IL-6, that induce production of more collagen, triggering platelets aggregation and activate coagulation cascade, and that may clinically lead to consequences similar to that caused by virus itself. Using IL-6 inhibitors such as Clazakizumab may lead to obtaining of vaccine safer than those used.