Alliance for Pandemic Preparedness

June 11, 2021

First-Dose ChAdOx1 and BNT162b2 COVID-19 Vaccines and Thrombocytopenic, Thromboembolic and Hemorrhagic Events in Scotland

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  • Compared to those who received one dose of the Pfizer-BioNTech COVID-19 vaccine, receipt of one dose of the Oxford-AstraZeneca vaccine was associated with a higher risk of idiopathic thrombocytopenic purpura (ITP), a blood disorder involving low platelet counts, during 0–27 days after vaccination (adjusted RR = 5.8), with an estimated incidence of 1.13 cases per 100,000 doses. Findings were based on a nested, incident-matched case-control study (N=2.5 million) conducted in Scotland. Confirmatory self-controlled case series analysis confirmed this association was unlikely to be due to bias, although the true risk ratio is likely lower (RR=1.2) due to the potential for overestimation of reported results due to residual confounding. Receipt of the Pfizer-BioNTech vaccine was not associated with ITP. The authors suggest that using an alternative to the AstraZeneca vaccines may be appropriate for individuals at low risk of COVID-19 if supply allows.

Simpson et al. (June 2021). First-Dose ChAdOx1 and BNT162b2 COVID-19 Vaccines and Thrombocytopenic, Thromboembolic and Hemorrhagic Events in Scotland. Nature Medicine. https://doi.org/10.1038/s41591-021-01408-4