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A range of studies have suggested that blood group and risk for severe COVID-19 are linked. Using a national database between 2007 and 2019 in Ontario, Canada, investigators analyzed the proportions of persons with SARS-CoV-2 infection and severe COVID-19 for whom blood group information was available.
Among 225,556 eligible participants (mean age, 54; 29% men) who had undergone SARS-CoV-2 testing between January and June 2020, the adjusted risk ratio (aRR) for SARS-CoV-2 infection was 0.88 among persons with blood group O compared with all other groups, and 0.79 among those with blood group Rh− versus Rh+. The effect of blood group on probability of infection was more pronounced in those younger than 70. A total of 1328 COVID-19 cases were …