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BackgroundWhereas accumulating studies on COVID-19 patients report high incidences of thrombotic complications, large studies on clinically relevant thrombosis in patients with other respiratory tract infections are lacking. How this high risk in COVID-19 patients compares to those observed in hospitalized patients with other viral pneumonias such as influenza is unknown.ObjectivesTo assess the incidence of venous and arterial thrombotic complications in hospitalized influenza patients as opposed to that observed in hospitalized COVID-19 patients.MethodsRetrospective cohort study; we used data from Statistics Netherlands (study period: 2018) on thrombotic complications in hospitalized influenza patients. In parallel, we assessed the cumulative incidence of thrombotic complications – adjusted for competing risk of death - in patients with COVID-19 in three Dutch hospitals (February 24th - April 26th 2020).ResultsOf the 13.217 hospitalized influenza patients, 437 (3.3%) were diagnosed with thrombotic complications, versus 66 (11%) of the 579 hospitalized COVID-19 patients. The 30-day cumulative incidence of any thrombotic complication in influenza was 11% (95%CI 9.4-12) versus 25% (95%CI 18-32) in COVID-19. For venous thrombotic complications (VTE) and arterial thrombotic complications alone, these numbers were respectively 3.6% (95%CI 2.7-4.6) and 7.5% (95%CI 6.3-8.8) in influenza versus 23% (95%CI 16-29) and 4.4% (95%CI 1.9-8.8) in COVID-19.ConclusionsThe incidence of thrombotic complications in hospitalized influenza patients was lower than in hospitalized COVID-19 patients. This difference was mainly driven by a high risk of VTE complications in the COVID-19 patients admitted to ICU. Remarkably, influenza patients were more often diagnosed with arterial thrombotic complications.EssentialsIt is unknown how COVID-19 compares to patients with other virus infections regarding thrombosis.Hospitalized patients with influenza and COVID-19 were evaluated and compared to each other.30-day cumulative incidence of thrombosis was lower in influenza (11%) than in COVID-19 (25%).Difference was mainly driven by a high risk of VTE in COVID-19 patients admitted to the ICU.