ABO blood group association and COVID-19. COVID-19 susceptibility and severity: a review

INTRODUCTION: The SARS-CoV-2 pandemic has been affecting the health and economic, as well as social, life of the entire globe since the end of 2019. The virus causes COVID-19, with a wide range of symptoms among the infected individuals, from asymptomatic infection to mortality. This, along with a high infection rate, prompted efforts to investigate the potential mechanisms of the different clinical manifestations caused by SARS-CoV-2 among the infected populations. HYPOTHESIS: One of the possible mechanisms that has been reported is the ABO blood system polymorphism. Indeed, one of the major proposed mechanisms is the presence of naturally occurring anti-A antibodies in individuals of groups O and B, which could be partially protective against SARS-CoV-2 virions. OBJECTIVE AND METHOD: This article aimed to review the published data on the potential effect of the ABO blood group system on the susceptibility to COVID-19 and the disease progression and outcomes. RESULTS: The reviewed data suggest that individuals of blood group A are at a higher risk of infection with SARS-CoV-2 and may develop severe COVID-19 outcomes, whereas blood group O is considered protective against the infection, to some extent. However, some of the available studies seem to have been influenced by unaccounted confounders and biases. CONCLUSION: Therefore, further appropriately controlled studies are warranted to fully investigate the possible association between the ABO blood groups and COVID-19 susceptibility and severity.