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Some research has suggested an excess risk for COVID-19 in people with blood group type A and lower risk in people with type O blood. To explore this relation, researchers conducted a cohort study in a large integrated health system; they identified 107,000 patients (mean age, 42) whose blood type was noted in the medical record and who had been tested for SARS-CoV-2 infection (96,000 tested negative, and 11,000 tested positive).
Among people who tested positive, older age and male sex were associated significantly with worse clinical outcomes. In analyses adjusted for age and sex, no blood type group showed any association — neither increased nor decreased — with test positivity, hospitalization, or admission to an intensive care unit.
Anderson JL et al. Association of sociodemographic factors and blood group type with risk of COVID-19 in a US population. JAMA Netw Open 2021 Apr 5; 4:e217429. (https://doi.org/10.1001/jamanetworkopen.2021.7429)
Comment
The positive findings in this study for risk associated with age and sex strengthen the validity of the negative findings for blood group type. If any excess risk is associated with blood group type A, as suggested by prior studies, it appears to be markedly smaller than the risks associated with older age and male sex.