RETROSPECTIVE analysis of data of 93,906 patients hospitalised with either COVID-19 or influenza has shown that the risk of infection-associated venous thromboembolism (VTE) was greater for patients with COVID-19 compared with patients with influenza, irrespective of COVID-19 vaccine availability.
Leady study author Vincent Lo Re III, Perelman School of Medicine, University of Pennsylvania, Philadelphia, USA, and colleagues analysed data from 41,443 patients hospitalised with COVID-19 before vaccine availability (between April and November 2020); 44,194 patients hospitalised with COVID-19 between December 2020 and May 2021, whilst vaccines were available; and 8,269 patients hospitalised with influenza between October 2018 and April 2019. The study aim was to evaluate the 90-day risk of VTE (deep vein thrombosis and pulmonary embolism) and arterial thromboembolism (ischaemic stroke or myocardial infarction) between these groups.
The researchers found that the 90-day absolute risk for VTE was higher in both the pre– and post– vaccine availability COVID-19 groups than in the influenza group. The absolute risk for the post-vaccine availability COVID-19 group was 10.9% (95% confidence interval [CI]: 10.6–11.1); 9.5% (95% CI: 9.2–9.7%) in the pre-vaccine availability COVID-19 group; and 5.3% (95% CI: 4.9–5.8) in the influenza group.
The absolute risk difference between the post-vaccine availability COVID-19 and influenza groups and the pre-vaccine availability COVID-19 and influenza groups was 5.5% (95% CI: 5.0–6.1) and 4.1% (95% CI: 3.6–4.7), respectively. The adjusted hazard ratio between the influenza and post-vaccine COVID-19 and the influenza and pre-vaccine availability COVID-19 groups was 1.89 (95% CI: 1.68–2.12) and 1.6 (95% CI: 1.43–1.79), respectively, further highlighting the elevated prothrombotic risk associated with COVID-19.
No difference in the 90-day absolute risk for arterial thromboembolism was identified between either the pre-vaccine availability COVID-19 or the post-vaccine availability COVID-19 and influenza cohorts.
Ro Le III and colleagues postulated several explanations for these differences in VTE risk, including “heightened awareness of thrombosis with COVID-19” or “increased abundance of anti-phospholipid antibodies and enhanced platelet activity” secondary to the effect of severe acute respiratory syndrome coronavirus 2 on endothelial cells.
Whilst data on thrombotic event severity were unavailable, the findings from this research highlight the increased pro-thrombotic effect of COVID-19 compared with influenza, reiterating the importance of VTE prophylaxis in hospitalised patients.