HealthDay News — Type O and rhesus-negative (Rh−) blood groups seem to be associated with a lower risk for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, according to a study published online Nov. 24 in the Annals of Internal Medicine.

Joel G. Ray, M.D., from St. Michael’s Hospital in Toronto, and colleagues conducted a population-based cohort study to examine whether ABO and Rh blood groups are associated with SARS-CoV-2 infection and severe COVID-19 illness. Data were included for 225,556 individuals (mean age, 54 years) with ABO blood group assessed between January 2007 and December 2019.

The researchers found that the adjusted relative risk for SARS-CoV-2 infection was 0.88 for blood group O versus the A, AB, and B blood groups together. Rh− blood type was associated with a reduced risk for SARS-CoV-2 infection (adjusted relative risk, 0.79), especially for those who were O-negative (adjusted relative risk, 0.74). The risk for severe COVID-19 illness or death was lower in association with the type O blood group versus all others (adjusted relative risk, 0.87) and for Rh− versus Rh-positive (adjusted relative risk, 0.82).

“At most, a small proportion of SARS-CoV-2 infection or related illness in the entire population could be prevented by some undetermined property conferred by O blood type and, perhaps, further enhanced by Rh− status,” the authors write. “Whether this information can influence COVID-19 prevention or treatment strategies remains to be determined.”

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