1. Patients hospitalized due to COVID-19 had a higher risk of developing a venous thromboembolism within 90 days of admission than patients hospitalized due to influenza.

2. The risk of developing an arterial thromboembolism was not significantly different between patients hospitalized due to COVID-19 and influenza.

Level of Evidence Rating: 2 (Good)

Study Rundown: COVID-19 has caused millions of hospitalizations over the past few years, occasionally for extended periods of time and with a need for intensive care. Although it is primarily a respiratory virus, COVID-19 can cause systemic symptoms including a hypercoagulable state. The present study sought to determine the risk of arterial and venous thromboembolism in patients who were hospitalized due to COVID-19 versus influenza.

A total of 93,906 patients were included: 85,637 patients with COVID-19 and 8269 patients with influenza. In general, patients with COVID-19 were older, more racially diverse, more often male and had a higher comorbidity burden than influenza patients, although these differences were accounted for with weighted propensity matching in the analysis. The 90-day risk of arterial thromboembolism was 14.4% in the influenza cohort, 15.8% in the unvaccinated COVID group and 16.3% in the possibly vaccinated COVID group. This risk difference was not significant between the influenza and COVID groups. The 90-day risk of venous thromboembolism was 5.3% in the influenza cohort, 9.5% in the unvaccinated COVID group and 10.9% in the possibly vaccinated COVID group. This risk difference was significantly higher amongst patients hospitalized due to COVID compared to those with influenza.

This retrospective cohort study concluded that COVID-19 may increase the risk of venous thromboemboli compared to influenza amongst a cohort of hospitalized adults, although the risk of arterial thromboemboli is unchanged. Strengths of this study include the consistency of these results with previous work in this area, as well as the large sample size. However, the retrospective nature of this work limits the ability to draw conclusions about causality. Further study is needed to determine the mechanism of the correlation between venous thromboembolism and COVID-19.

Click here to read this study in JAMA

Relevant reading: Hypercoagulability in COVID-19: a review of the potential mechanisms underlying clotting disorders

In Depth [retrospective cohort]: A retrospective cohort study using data from the US Food and Drug Administration Sentinel System was conducted. This administrative database provides insurance claim data from 6 major insurers in the United States. Eligible patients were adults with a diagnosis of COVID-19 admitted to hospital between April 2020 and May 2021 and had at least one year of insurance coverage prior to hospitalization. The same criteria applied for the comparator group, except patients were diagnosed with influenza and hospitalized between October 2018 and April 2019. The primary outcomes were inpatient arterial and venous thromboemboli. The COVID cohort was further divided into those who were hospitalized prior to the introduction of vaccines (‘unvaccinated’) and those who were hospitalized after the introduction of vaccines (‘possibly vaccinated’).

The 90-day risk of arterial thromboembolism was 14.4% (95% confidence interval 13.6-15.2%) in the influenza cohort, 15.8% (15.5-16.2%) in the unvaccinated COVID group and 16.3% (16.0-16.6%) in the possibly vaccinated group. The risk of arterial thromboemboli was highest in each group amongst older, male patients who were admitted to the intensive care unit or required mechanical ventilation. However, the risk difference was not significantly different between patients with influenza and COVID: the adjusted hazard ratio for arterial thromboembolism in influenza versus unvaccinated COVID groups was 1.04 (0.97-1.11) and against the possibly vaccinated COVID group was 1.07 (1.00-1.14).

The 90-day risk of venous thromboembolism was 5.3% (4.9%-5.8%) in the influenza cohort, 9.5% (9.2%-9.7%) in the unvaccinated COVID group and 10.9% (10.6%-11.1%) in the possibly vaccinated group. The risk of venous thromboemboli was highest in each group amongst patients who had a history of venous thromboembolism, were admitted to the intensive care unit, or required mechanical ventilation. The risk difference was significantly different between patients with influenza and COVID: the adjusted hazard ratio for venous thromboembolism in influenza versus unvaccinated COVID groups was 1.60 (1.43-1.79) and against the possibly vaccinated COVID group was 1.89 (1.68-2.12).

Image: PD

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