An observational study to identify the prevalence of thrombocytopenia and anti‐PF4/polyanion antibodies in Norwegian health care workers after COVID‐19 vaccination

• Published in: Journal of thrombosis and haemostasis Vol. 19; no. 7; pp. 1813 - 1818
• Main Authors: Sørvoll, Ingvild Hausberg, Horvei, Kjersti Daae, Ernstsen, Siw Leiknes, Lægreid, Ingvild Jenssen, Lund, Svetlana, Grønli, Renathe Henriksen, Olsen, Magnus Kringstad, Jacobsen, Hege Karine, Eriksson, Anna, Halstensen, Anne Marie, Tjønnfjord, Eirik, Ghanima, Waleed, Ahlen, Maria Therese
• Format: Journal Article
• Language: English
• Published: England Elsevier Limited 01.07.2021; John Wiley and Sons Inc
• Subjects: Antibodies; Brief Report; Clinical trials; COVID-19; COVID-19 vaccines; COVID‐19 vaccines/adverse effects; drug related side effects and adverse reactions; Health care; Immunoassay; Medical personnel; Observational studies; Optical density; Platelet factor 4; PLATELETS; Severe acute respiratory syndrome coronavirus 2; Side effects; Thrombocytopenia; Thrombosis; Vaccines; COVID-19 vaccines; COVID-19 vaccines/adverse effects; platelet factor 4; thrombocytopenia; drug related side effects and adverse reactions
• ISSN: 1538-7933; 1538-7836; 1538-7836
• DOI: 10.1111/jth.15352

Background The 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. Objectives To investigate prevalence of thrombocytopenia and anti‐PF4/polyanion antibodies in a population recently vaccinated with AZD1222. Patients/Methods Four 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. Results The 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. Conclusions We found low prevalence of both thrombocytopenia and antibodies to PF4/polyanion‐complexes among Norwegian health care workers after vaccination with AZD1222.