Blood group O has been associated with decreased risk of SARS-CoV-2 infection in several small studies. In order to confirm these observations and determine if other blood groups are associated with SARS-CoV-2 infection, researchers in Denmark utilized data from the nationwide SCANDAT database. SCANDAT is a complete database of all Danish blood donors, including data on SARS-CoV-2 PCR and antigen tests, sex, age, and more than a dozen blood groups. Using data from SCANDAT from February 2020 to August 2021, 36,068 of 650,156 Danish blood donors tested positive for SARS-CoV-2. In a multivariable analysis that included adjustment for age and sex, two antigens—blood type O and Lewis Lea—were associated with a lower odds of SARS-CoV-2 infection. The odds of infection for blood types B, A, and AB compared to O were 1.10 (95% C.I., 1.06 to 1.14), 1.17 (95% C.I., 1.14 to 1.20), and 1.20 (95% C.I. 1.14 to 1.26), respectively. The odds of infection for the non-secretor Lewis phenotype Lea was 0.88 (95% C.I., 0.78 to 0.99) compared to the secretor phenotype where the ABO blood group antigens are present in other body fluids including mucus. No associations were found between blood groups and hospitalization or long-COVID. Further research is needed to understand the mechanisms of blood groups and COVID-19 susceptibility.
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