In the 90 days after hospitalization, patients with COVID-19 had similar risk of arterial thromboembolism but higher risk of venous thromboembolism (VTE) compared to patients with influenza.
A retrospective cohort study used the FDA Sentinel System to compare 41,443 patients hospitalized with COVID-19 before vaccine availability (April to November 2020), 44,194 hospitalized with COVID-19 during vaccine availability (December 2020 to May 2021), and 8,269 patients hospitalized with influenza in October 2018 to April 2019. Results were published by JAMA on Aug. 16.
The three groups had similar 90-day risk of arterial thromboembolism (acute myocardial infarction or stroke): 14.4% (95% CI, 13.6% to 15.2%) in patients with flu, 15.8% (95% CI, 15.5% to 16.2%) in patients with COVID-19 before vaccines, and 16.3% (95% CI, 16.0% to 16.6%) in patients with COVID-19 after vaccines (adjusted hazard ratios [HRs], 1.04 [95% CI, 0.97 to 1.11] between flu and before-vaccine COVID-19 and 1.07 [95% CI, 1.00 to 1.14] between flu and after-vaccine COVID-19).However, the 90-day absolute risk of VTE was 5.3% (95% CI, 4.9% to 5.8%) in patients with influenza versus 9.5% (95% CI, 9.2% to 9.7%) in patients with COVID-19 before vaccines and 10.9% (95% CI, 10.6% to 11.1%) in patients with COVID-19 after vaccines (adjusted HRs, 1.60 [95% CI, 1.43 to 1.79] and 1.89 [95% CI, 1.68 to 2.12], respectively).
The authors noted that further research is needed to understand the mechanisms behind the increased risk of VTE with COVID-19, but they offered some possible reasons. “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,” they wrote. Another possibility is that early research indicating a risk of thrombosis in COVID-19 might have led to increased identification of clots, but that would not explain why there was a link between the virus and VTE but not arterial thromboembolism, the authors said. Among other limitations, data on COVID-19 or influenza immunization status were not included.
In other COVID-19 news, the NIH recently updated its treatment guidelines, including recommendations on therapeutic management of hospitalized adults with COVID-19. Among other changes, the guidance now recommends that patients who are found to have mild to moderate COVID-19 while hospitalized for other reasons and who have high risk of progression should be treated according to the guidelines for outpatients with COVID-19. Other updates address use of immunomodulators in inpatients.