Risk for VTE higher with COVID-19 than influenza
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Compared with patients hospitalized with influenza, patients hospitalized with COVID-19, both before and during vaccine availability, had elevated risk for venous thromboembolism, researchers reported in JAMA.
There was no difference between patients with COVID-19 and patients with influenza in risk for arterial thromboembolism.
The researchers analyzed 41,443 patients with COVID-19 hospitalized from April to November 2020, before vaccine availability; 44,194 patients with COVID-19 hospitalized from December 2020 to May 2021, during vaccine availability; and 8,269 patients hospitalized with influenza from October 2018 to April 2019.
The primary outcomes were VTE, defined as deep vein thrombosis or pulmonary embolism, and arterial thromboembolism, defined as acute MI or ischemic stroke, at 90 days.
The mean age of all cohorts was 72 years. The COVID-19 population comprised 51% men and the influenza population comprised 45% men.
90-day risks
The 90-day absolute risk for arterial thromboembolism was 14.4% (95% CI, 13.6-15.2) in the influenza population, 15.8% (95% CI, 15.5-16.2) in the pre-vaccine COVID-19 population and 16.3% (95% CI, 16-16.6) in the post-vaccine COVID-19 population, Vincent Lo Re III, MD, MSCE, associate professor of medicine and epidemiology at Perelman School of Medicine at the University of Pennsylvania, and colleagues wrote.
The absolute risk difference between the influenza population and the pre-vaccine COVID-19 population was 1.4% (95% CI, 1-2.3), and the absolute risk difference between the influenza population and the post-vaccine COVID-19 population was 1.9% (95% CI, 1.1-2.7), and after adjustment, there was no difference in risk for arterial thromboembolism between the influenza population and the pre-vaccine COVID-19 population (adjusted HR = 1.04; 95% CI, 0.97-1.11) or between the influenza population and the post-vaccine COVID-19 population (aHR = 1.07; 95% CI, 1-1.14), according to the researchers.
The 90-day absolute risk for VTE was 5.3% (95% CI, 4.9-5.8) in the influenza population, 9.5% (95% CI, 9.2-9.7) in the pre-vaccine COVID-19 population and 10.9% (95% CI, 10.6-11.1) in the post-vaccine COVID-19 population, Lo Re and colleagues wrote.
The absolute risk difference between the influenza population and the pre-vaccine COVID-19 population was 4.1% (95% CI, 3.6-4.7), and the absolute risk difference between the influenza population and the post-vaccine COVID-19 population was 5.5% (95% CI, 5-6.1), and after adjustment, and COVID-19 in the pre-vaccine era (aHR = 1.6; 95% CI, 1.43-1.79) and COVID-19 in the post-vaccine era (aHR = 1.89; 95% CI, 1.68-2.12) both conferred more risk for VTE compared with influenza, according to the researchers.
Possible reasons
“There are several possible reasons for the higher risk of venous thromboembolism among patients with COVID-19 compared with influenza,” Lo Re and colleagues wrote. “SARS-CoV-2 infection of endothelial cells incites inflammation and abnormalities in coagulation, such as an increased abundance of antiphospholipid antibodies and enhanced platelet activity. These abnormalities might be more marked in patients with COVID-19 vs. in patients with influenza infections. Alternatively, heightened awareness of thrombosis with COVID-19 might have led to a greater ascertainment of events in patients with COVID-19 after case series published early in the pandemic reported high rates of these complications. However, no association between COVID-19 and arterial thromboembolism was observed, which might be subject to similarly increased event ascertainment.”
In addition, they wrote, “Patients with COVID-19 may have had a higher frequency of thromboses that contributed to organ failure, multisystem injury and death (eg, more pulmonary embolism than deep vein thrombosis) compared with patients with influenza. However, data regarding the severity of the thrombotic events were not available in this study.”
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