Thrombocytopenia and Vaccines Links

https://www.medrxiv.org/content/10.1101/2021.07.23.21261036v1 Abstract Background  Covid-19 vaccines may increase the risk of venous thromboembolism (VTE), thrombocytopenia (TCP), and VTE associated with TCP. We aimed at estimating this risk by age and sex, after the first dose of both adenovirus vector-based and mRNA-based Covid-19 vaccines, and after the second dose of m-RNA vaccines. Methods  In this population-based retrospective cohort study, we examined three groups: 1 662 719 people 10 years of age and over vaccinated with the first dose of a Covid-19 vaccine, 622 778 with the second dose, and 190 616 diagnosed of Covid-19 in the same period (between1 January 2021 and 18 April 2021). The rates of various clinical presentations of VTE and TCP were compared with those in the reference population (7 013 040 people served by the health care system in 2919). The two primary outcomes were the observed 21 day rate of a composite variable of cerebral venous sinus thrombosis, m...

 https://www.ahajournals.org/doi/10.1161/STROKEAHA.121.035613 Cerebral Vein Thrombosis With Vaccine-Induced Immune Thrombotic Thrombocytopenia Abstract In the spring of 2021, reports of rare and unusual venous thrombosis in association with the ChAdOx1 and Ad26.COV2.S adenovirus-based coronavirus vaccines led to a brief suspension of their use by several countries. Thromboses in the cerebral and splanchnic veins among patients vaccinated in the preceding 4 weeks were described in 17 patients out of 7.98 million recipients of the Ad26.COV2.S vaccine (with 3 fatalities related to cerebral vein thrombosis) and 169 cases of cerebral vein thrombosis among 35 million ChAdOx1 recipients. Events were associated with thrombocytopenia and anti-PF4 (antibodies directed against platelet factor 4), leading to the designation vaccine-induced immune thrombotic thrombocytopenia. Unlike the related heparin-induced thrombotic thrombocytopenia, with an estimated incidence of <1:1000 patients treat...

 https://www.nejm.org/doi/full/10.1056/NEJMoa2104840 Abstract BACKGROUND Several cases of unusual thrombotic events and thrombocytopenia have developed after vaccination with the recombinant adenoviral vector encoding the spike protein antigen of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (ChAdOx1 nCov-19, AstraZeneca). More data were needed on the pathogenesis of this unusual clotting disorder. METHODS We assessed the clinical and laboratory features of 11 patients in Germany and Austria in whom thrombosis or thrombocytopenia had developed after vaccination with ChAdOx1 nCov-19. We used a standard enzyme-linked immunosorbent assay to detect platelet factor 4 (PF4)–heparin antibodies and a modified (PF4-enhanced) platelet-activation test to detect platelet-activating antibodies under various reaction conditions. Included in this testing were samples from patients who had blood samples referred for investigation of vaccine-associated thrombotic events, with 28 test...