SARS-CoV-2 vaccines are not associated with hypercoagulability in apparently healthy people.

Background: SARS-CoV-2 adenoviral-vector-DNA vaccines have been linked to the rare but serious thrombotic post-vaccine complication vaccine-induced immune thrombotic thrombocytopenia (VITT). This has raised concerns regarding the possibility of increased thrombotic risk after any SARS-CoV-2 vaccines. Objectives: To investigate whether SARS-CoV-2 vaccines cause coagulation activation leading to a hypercoagulable state. Methods: This observational study included 567 healthcare personnel, 521 were recruited post-vaccination after a first dose of adenoviral vector ChAdOx1-S (Vaxzevria®, AstraZeneca) vaccine, and 46 prospectively before vaccination with an mRNA vaccine, either Spikevax® (Moderna, n=38) or Comirnaty® (Pfizer-BioNTech, n=8). In the mRNA group, samples were acquired before and 1-2 weeks after vaccination. In addition to pre-vaccination samples, 56 unvaccinated blood donors were recruited as controls (total n=102). Thrombin generation, D-dimer and free tissue factor pathway inhibitor (TFPI) were analyzed. Results: No participant experienced thrombosis, VITT or thrombocytopenia (platelet count <100·109/L) one week to one month post-vaccination. There was no increase in thrombin generation, D-dimer or TFPI in the ChAdOx1-S vaccine group compared with controls, or after the mRNA vaccines compared with baseline values. Eleven of 513 vaccinated with ChAdOx1-S (2.1%) had anti-PF4/polyanion antibodies without concomitant increase in thrombin generation. Conclusion: In this study, SARS-CoV-2 vaccines were not associated with thrombosis, thrombocytopenia, increased thrombin generation, D-dimer or TFPI levels compared with baseline or unvaccinated controls. These findings argue against subclinical activation of coagulation post-COVID-19 vaccination.

Thromboembolic complications during and after hospitalization for COVID-19: Incidence, risk factors and thromboprophylaxis

Introduction The incidence of thromboembolism during COVID-19 and the use of thromboprophylaxis vary greatly between studies. Only a few studies have investigated the rate of thromboembolism post-discharge. This study determined the 90-day incidence of venous and arterial thromboembolic complications, risk factors for venous thromboembolic events and characterized the use of thromboprophylaxis during and after hospitalization. Materials and methods We retrospectively reviewed medical records for adult patients hospitalized for >24 hours for COVID-19 before May 15, 2020, in ten Norwegian hospitals. We extracted data on demographics, thromboembolic complications, thromboembolic risk factors, and the use of thromboprophylaxis. Cox proportional hazards regression was used to determine risk factors for VTE. Results 550 patients were included. The 90-day incidence of arterial and venous thromboembolism in hospitalized patients was 6.9% (95% CI: 5.1–9.3) overall and 13.8% in the ICU. Male sex (hazard ratio (HR) 7.44, 95% CI 1.73–32.02, p = 0.007) and previous VTE (HR 6.11, 95% CI: 1.74–21.39, p = 0.005) were associated with risk of VTE in multivariable analysis. Thromboprophylaxis was started in 334 patients (61%) with a median duration of 7 days (25th–75th percentile 3–13);in the VTE population 10/23 (43%) started thromboprophylaxis prior to diagnosis. After discharge 20/223 patients received extended thromboprophylaxis and 2/223 (0.7%, 95% CI: 0.3–1.9) had a thromboembolism. Conclusions The 90-day incidence of thromboembolism in COVID-19 patients was 7%, but <1% after discharge. Risk factors were male sex and previous VTE. Most patients received thromboprophylaxis during hospitalization, but only <10% after discharge.