Publication date: Oct 15, 2024

COVID-19 is a strong risk factor for venous thromboembolism (VTE). Few studies have evaluated the effectiveness of COVID-19 vaccination in preventing hospitalization for COVID-19 with VTE. Adults hospitalized at 21 sites between March 2021 and October 2022 with symptoms of acute respiratory illness were assessed for COVID-19, completion of the original monovalent mRNA COVID-19 vaccination series, and VTE. Prevalence of VTE was compared between unvaccinated and vaccinated patients with COVID-19. Vaccine effectiveness in preventing COVID-19 hospitalization with VTE was calculated using a test negative design. Vaccine effectiveness was also stratified by predominant circulating SARS-CoV-2 variant. Among 18,811 patients (median age 63 [IQR:50-73], 49% women, 59% non-Hispanic White, 20% non-Hispanic Black, 14% Hispanic, and median of 2 comorbid conditions [IQR:1-3]), 9,792 were admitted with COVID-19 (44% vaccinated) and 9,019 were test-negative controls (73% vaccinated). Among patients with COVID-19, 601 were diagnosed with VTE by hospital day 28, of whom 170 were vaccinated. VTE was more common among unvaccinated than vaccinated COVID-19 patients (7. 8% versus 4. 0%; p=0. 001). Vaccine effectiveness against COVID-19 hospitalization with VTE was 84% (95% CI: 80-87%) overall. Vaccine effectiveness stratified by predominant circulating variant was 88% (73-95%) for alpha, 93% (90-95%) for delta, and 68% (58-76%) for omicron variants. Vaccination with the original monovalent mRNA series was associated with a decrease in COVID-19 hospitalization with VTE, though data detailing prior history of VTE and use of anticoagulation were not available. These findings will inform risk-benefit considerations for those considering vaccination.

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