Thrombosis and bleeding after COVID-19 vaccination: do differences in sex matter?

Gender medicine deals with differences in approach to diagnostic work-up and management according to gender. Although the issue is relevant in every field of medicine, it is often neglected. However, the recent SARS-CoV-2 pandemic has made consideration of gender even more urgent. In fact, available literature has suggested a higher number of deaths among infected men than in women and more side effects in women than in male recipients of certain anti-COVID-19 vaccines. This review examines sex-disaggregated data on thrombotic and bleeding events associated with vaccination against COVID-19. Thrombotic complications are by far more frequently reported than bleeding events after vaccination and are mostly observed in young women receiving viral-vectored vaccines. However, detailed data that could help better stratify the risk according to sex/gender are generally lacking. Likewise, overall bleeding complications and those associated with a specific vaccine are mainly reported as aggregated data, including thrombocytopenia that is reported to occur in the presence or absence of thrombotic complications. Such information is important as it underlines the need to differentiate between thrombocytopenia with and without thrombosis because management and prognosis differ according to the association of thrombotic events. Here, we highlight how the lack of disaggregated data has led to the publication of conflicting information about adverse events by sex in recipients of viral-vectored vaccines. Lastly, we examine the possible mechanisms underlying vaccine-associated thrombotic and bleeding complications according to sex/gender.