No apparent association between mRNA COVID-19 vaccination and venous thromboembolism

By January 2022 over ten billion doses of COVID-19 vaccines had been administered worldwide. Concerns about COVID-19 vaccine-associated thrombosis arose after the characterization of a rare prothrombotic condition associated with adenoviral vector-based COVID-19 vaccines known as vaccine-induced immune thrombotic thrombocytopenia (VITT). Although mRNA COVID-19 vaccines have not been linked to VITT, concerns about thrombosis after vaccination persist despite safety data from hundreds of millions of recipients of mRNA COVID-19 vaccines. With widespread vaccination some VTE will occur shortly after vaccination by chance alone because VTE is a common condition that affects 1 to 2 in 1000 persons each year. Detailed analysis is required to determine whether these VTE events are coincidental or associated when they occur in close proximity to mRNA vaccine administration. This paper will review what is currently known about rates of VTE after mRNA vaccination in adults, discuss the reasons why uncertainty on this topic persists, and briefly review the implications of these findings for clinical practice and health policy.