Effectiveness of the Original Monovalent Messenger RNA Coronavirus Disease 2019 (COVID-19) Vaccination Series Against Hospitalization for COVID-19-Associated Venous Thromboembolism.

Abstract

Coronavirus disease 2019 (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 messenger RNA (mRNA) COVID-19 vaccination series, and VTE. Prevalence of VTE was compared between unvaccinated and vaccinated patients with COVID-19. The vaccine effectiveness (VE) in preventing COVID-19 hospitalization with VTE was calculated using a test-negative design. The VE was also stratified by predominant circulating severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant. Among 18 811 patients (median age [interquartile range], 63 [50-73] years; 49% women; 59% non-Hispanic white, 20% non-Hispanic black, and 14% Hispanic; and median of 2 comorbid conditions [interquartile range, 1-3]), 9792 were admitted with COVID-19 (44% vaccinated), and 9019 were test-negative controls (73% vaccinated). Among patients with COVID-19, 601 had VTE diagnosed by hospital day 28, of whom 170 were vaccinated. VTE was more common among unvaccinated than vaccinated patients with COVID-19 (7.8% vs 4.0%; P = .001). The VE against COVID-19 hospitalization with VTE was 84% overall (95% confidence interval, 80%-87%), and VE 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.