Rationale and background: In March 2021, cases of thrombotic events associated with thrombocytopenia began to appear after the administration of AstraZeneca's COVID-19 vaccine. Although the risk following administration of AstraZeneca and Janssen vaccines for these thrombotic or embolic disorders with and without thrombocytopenia, as well as for thrombocytopenia without associated thromboembolism, has been established, it has not yet been fully characterised and quantified. Objectives: To quantify the association between the occurrence of thromboembolic events and thrombocytopenia, separately and thromboembolism together with thrombocytopenia and the administration of COVID-19 vaccines. Data source: BIFAP (Base de datos para la Investigación Farmacoepidemiológica en el Ámbito Público). Study design: A self-controlled case series (SCCS) design with pre- and post-vaccine control intervals as the main analysis. Also, exploratory analyses will be conducted: firstly, using an SCCS design with a post-vaccine control interval only, and secondly, using a self-controlled risk interval (SCRI) design. The study period will be from September 1st, 2020, until death, patient exit from the database, or end of study. Population: All individuals aged ≥5 years, registered with their primary care physician for at least 365 days, who have received one of the following COVID-19 vaccines: AstraZeneca, Pfizer, Moderna, or Janssen and for whom any of the defined outcomes of interest have been identified. Events of interest: Venous thromboembolism, arterial thromboembolism, and thrombocytopenia, as well as concomitance of thromboembolism with thrombocytopenia. Data analysis: Description of the study population characteristics. For all study designs, we will compare the event rates in the post-vaccination risk period with the control periods using conditional Poisson regression, by type of vaccine.