Reactions 1871, p12 - 4 Sep 2021Thrombocytopenia and thromboembolism after COVID-19 vaccination

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Reactions 1871, p12 - 4 Sep 2021

Thrombocytopenia and thromboembolism after COVID-19 vaccination

Risks of thrombocytopenia and venous thromboembolism are increased after vaccination with the Oxford- AstraZeneca COVID-19 vaccine [AZD-1222; ChAdOx1 nCoV-19], while the risk of arterial thromboembolism is increased after vaccination with the Pfizer-BioNTech COVID-19 vaccine [tozinameran; BNT162b2]. These were findings of a self-controlled case series study published in the BMJ.¹

Data on deaths from the UK Office for National Statistics, COVID-19 (SARS-CoV-2) positive test data, and data on hospital admissions from the National Health Service, along with electronic health records were used to investigate adverse events in England between December 2020 and April 2021 after a first dose of the AstraZeneca vaccine (n=19 608 008) or Pfizer vaccine (9 513 625), or after a positive COVID-19 test (1 758 095).

The AstraZeneca vaccine was associated with an increased risk of thrombocytopenia (incidence rate ratio [IRR] 1.33;

95% CI 1.19, 1.47), venous thromboembolism (IRR 1.10; 1.02, 1.18), cerebral venous sinus thrombosis (CVST;

IRR 4.01; 95% CI 2.08, 7.71), and other rare arterial thrombotic events (IRR 1.21; 1.02, 1.43), after 8–14 days.

The Pfizer vaccine was associated with an increased risk of arterial thromboembolism (IRR 1.06; 95% CI 1.01, 1.10), CVST (IRR 3.38; 95% CI 1.39, 9.27) and ischaemic stroke (IRR 1.12; 95% CI 1.04, 1.20), after 15-21 days.

COVID-19 infection was associated with an increased risk of thrombocytopenia (IRR 5.27; 95% CI 4.34, 6.40) and venous thromboembolism (IRR 13.86; 95% CI 12.76, 15.05) at 8-14 days, and an increased risk of arterial thromboembolism (IRR 2.02;95% CI 1.8, 2.24) at 15-21 days. Risks of CVST, ischaemic stroke and other rare arterial thrombotic events were also increased in COVID-19-positive patients.

"Increased risks of some adverse thrombotic events leading to hospital admission or death were observed in the 28 days after first doses of vaccines. The risks of most of these events were substantially higher and more prolonged after SARS-Cov-2 infection," said the authors.

"This analysis included only vaccinated participants, and rates of these events would likely be higher in unvaccinated people with SARS-CoV-2 infection, again suggesting a net positive benefit-risk balance in favour of vaccination,"

commented Professors Olaf Klungel and Anton Pottegard, from Utrecht, Netherlands and Odense, Denmark, respectively, in an accompanying editorial published in the BMJ.² "A massive effort is underway from regulatory agencies worldwide to accelerate the assessment of benefit-risk balance and harmonise protocols for evaluating the safety of covid-19 vaccines," they said.

1. Hippisley-Cox J, et al. Risk of thrombocytopenia and thromboembolism after covid-19 vaccination and SARS-CoV-2 positive testing: self-controlled case series study BMJ : 27 Aug 2021. Available from: URL: https://doi.org/10.1136/bmj.n1931.

2. Klungel OH, et al. Strengthening international surveillance of vaccine safety BMJ : 27 Aug 2021. Available from: URL: https://doi.org/10.1136/bmj.n1994.

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