Clinical and Serological Characteristics of Vaccine-Associated Immune Thrombocytopenia Following COVID-19 Vaccination

Vaccine-associated immune thrombocytopenia (VA-ITP) is a serious complication following vaccination where the body's immune system mistakenly attacks and destroys platelets, the cells responsible for blood clotting. This significantly decreases platelet count and increases bleeding risk. The best described association between a vaccine and VA-ITP is the measles-mumps-rubella vaccine (MMR) in children. Although VA-ITP was reported during COVID-19 vaccine campaigns and continues to complicate vaccine safety, its exact cause and long-term outcomes are not well understood. This study aims to evaluate the clinical and laboratory outcomes of patients who developed VA-ITP after receiving COVID-19 vaccines. In particular, the investigators aim to evaluate the association of VA-ITP with anti-platelet antibodies. The investigators will identify adult patients from a thrombocytopenia registry at McMaster University and analyze their platelet counts, vaccine history, treatments, and the presence of specific platelet antibodies that could explain the condition. The investigators' goal is to determine whether certain patients with VA-ITP have more severe disease and whether certain vaccines are associated with a more severe clinical course. The investigators' findings will help improve the understanding of VA-ITP and guide development of better treatment strategies. This is especially important for ensuring vaccine safety and maintaining public confidence in vaccines for infectious diseases like COVID-19.