In a large real-world study, data published as a pre-print on The Lancet server from over one million individuals assessed the incidence rates of blood clotting disorders of thromboembolism and thrombocytopenia, including the very rare thrombosis with thrombocytopenia (TTS) following vaccination with an mRNA vaccine or Vaxzevria, and compared them with expected rates in a general population and in people with COVID-19.