Association of Sociodemographic Factors and Blood Group Type With Risk of COVID-19 in a US Population.

The observed variability in susceptibility to SARS-CoV-2 and severity of the ensuing COVID-19 have raised intense interest in their environmental and genetic risk factors. An early report from China1 suggested that blood group A was associated with increased susceptibility and blood group O was associated with reduced susceptibility to SARS-CoV-2 infection. These reports motivated widespread interest in examining ABO blood groups as potential COVID-19 risk factors. Subsequent studies from Italy and Spain2 reported that blood group A was associated with an increased risk of severe COVID-19 and blood group O was associated with a reduced risk. In contrast, a large Danish study3 implicated disease susceptibility but not severity. However, observations from Boston, Massachussets,4 and New York, New York,5 did not confirm any specific associations between ABO blood group and disease. The controversy raised by these contrasting reports led to this case-control study.