Inclusion Criteria:  Informed consent as documented by signature Newly diagnosed primary ITP according to the definition of Rodeghiero et al. and a risk of platelet count of <30x109/l or risk of severe bleeding No previous treatment for ITP No steroids in the last 4 weeks (for other conditions) Bleeding severity and quality of life are neither an inclusion nor an exclusion criterion.  Exclusion Criteria:  Patients previously treated for ITP (e.g. Steroid, intravenous immunoglobulin (IVIG), platelet infusion) Life-threatening bleeding (and inability to sign informed consent) Secondary ITP Positive family history for ITP Presence or history of autoimmune disease as judged by the investigator Hepatosplenomegaly in the clinical examination Relevant hepatic disease as judged by the investigator Presence or history of thromboembolic disease Patients with splenectomy Women who are pregnant or breast feeding Intention to become pregnant during the course of the study Lack of safe double contraception Any vaccination 2 weeks prior start of the study Immunsuppressive and antiplatelet drugs Known or suspected non-compliance, drug or alcohol abuse Inability to follow the procedures of the study, e.g. due to language problems, psychological disorders, incompetence to judge Participation in another study with investigational drug within the 30 days preceding and during the present study Enrolment of the investigator, his/her family members, employees and other dependent persons