The relative protective effects of O, Rh-, and O- blood groups were greatest in patients younger than age 70. Results also indicated the aRR for SARS-CoV-2 infection was higher in patients with AB blood type compared with type A. Comparatively, the highest unadjusted probability of SARS-CoV-2 infection was in the B+ blood group (4.2% 95% CI, 4.0-4.5%). The aRR for SARS-CoV-2 infection in the O blood group was 0.88 (95% CI, 0.84-0.92) vs all other blood groups, and the ARD was -3.9 per 1,000 (95% CI, -5.4 to -2.5).

The O- blood group had a 2.1% chance of getting SARS-CoV-2 infection (95% CI, 1.8-2.3%), the lowest unadjusted probability of all blood groups. For the primary outcome, analyses were further stratified by patients aged younger than 70 years vs 70 years or older. Adjusted relative risks (aRRs) and absolute risk differences (ARDs) were adjusted for demographic characteristics and comorbidities. The secondary outcome was severe COVID-19 illness or death. The study’s primary outcome was SARS-CoV-2 infection. Common comorbidities included preexisting cardiac disease (13-15%), chronic kidney disease (11%), anemia (21%), cancer (27-29%), dementia or frailty (33-38%), diabetes mellitus (21%), asthma (18-21%), and chronic hypertension (39-41%).

The mean age was 53.8 years and 29% were men. Investigators conducted a population-based, retrospective cohort study of 225,556 patients who had their ABO blood group assessed between January 2007 and December 2019, and subsequently tested for SARS-CoV-2 between January 15 and June 30, 2020. Patients with type O and rhesus negative (Rh-) blood groups may have a lower risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and severe coronavirus disease 2019 (COVID-19) illness, according to a study published in the Annals of Internal Medicine.

O negative blood