In order to help public health authorities and clinicians to contextualize observed events of vaccine-induced immune thrombotic thrombocytopenia (VITT) – an extremely rare but serious blood clot following immunization with the AstraZeneca/Vaxzevria COVID-19 vaccine – the Canadian Immunization Research Network (CIRN), including CITF-funded researcher Dr. Jeff Kwong, sought to estimate background rates of selected thromboembolic and coagulation disorders in Ontario from 2015-2020.