• Ingvild Hausberg Sørvoll, Kjersti Daae Horvei, Siw Leiknes Ernstsen, Ingvild Jenssen Laegreid, Svetlana Lund, Renathe Henriksen Grønli, Magnus Kringstad Olsen, Hege Karine Jacobsen, Anna Eriksson, Anne Marie Halstensen, Eirik Tjønnfjord, Waleed Ghanima, and Maria Therese Ahlen.
• Norwegian National Unit for Platelet Immunology, Department of Laboratory Medicine, University Hospital of North Norway, Tromsø, Norway.
• J. Thromb. Haemost. 2021 Jul 1; 19 (7): 1813-1818.

BackgroundThe COVID-19 vaccine from AstraZeneca (AZD1222) is one of several vaccines introduced to provide immunity against SARS-CoV-2. Recently, more than 50 cases have been reported presenting a combination of thrombosis, thrombocytopenia, and remarkably high levels of anti-platelet factor 4 (PF4)/polyanion antibodies post-AZD1222 vaccination. Now linked to the vaccine, the condition is referred to as vaccine-induced immune thrombotic thrombocytopenia. The European Medicines Agency still recommends vaccination with AZD1222, but several European countries have temporally paused and/or restricted its use because of the perceived risk of this severe side effect. Because there is no description of PF4/polyanion antibody testing in the clinical trials, knowledge about the prevalence of such antibodies in a vaccinated cohort is needed.ObjectivesTo investigate prevalence of thrombocytopenia and anti-PF4/polyanion antibodies in a population recently vaccinated with AZD1222.Patients/MethodsFour hundred and ninety-two health care workers recently vaccinated with the first dose of AZD1222 were recruited from two hospitals in Norway. Study individuals were screened for thrombocytopenia and the presence of anti-PF4/polyanion antibodies with a PF4/PVS immunoassay. Side effects after vaccination were registered.ResultsThe majority of study participants had normal platelet counts and negative immunoassay. Anti-PF4/polyanion antibodies without platelet activating properties were only detected in six individuals (optical density ≥0.4, range 0.58-1.16), all with normal platelet counts. No subjects had severe thrombocytopenia.ConclusionsWe found low prevalence of both thrombocytopenia and antibodies to PF4/polyanion-complexes among Norwegian health care workers after vaccination with AZD1222.© 2021 The Authors. Journal of Thrombosis and Haemostasis published by Wiley Periodicals LLC on behalf of International Society on Thrombosis and Haemostasis.

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