Blood group O was associated with a decreased risk for contracting SARS-CoV-2 infection, according to the results of large retrospective analysis of the Danish population.
Researchers Mike Bogetofte Barnkob, MD, of the Department of Clinical Immunology, Odense (Denmark) University Hospital, and colleagues performed a retrospective cohort analysis of all Danish individuals with a known ABO blood group who were tested for SARS-CoV-2 between Feb. 27, 2020, and July 30, 2020.
Of the 841,327 people tested, ABO and RhD blood groups could be identified for 473,654 individuals. ABO and RhD data from 2,204,742 (38% of the entire Danish population) were used as a reference, according to the online report in Blood Advances.
The primary outcome was status of ABO and RhD blood groups and test results for SARS-CoV-2. The secondary outcomes followed were hospitalization and death from COVID-19.
Reduced prevalence
The study found that ABO blood groups varied significantly between patients and the reference group, with only 38.41% (95% confidence interval, 37.30%-39.50%) of the patients belonging to blood group O, compared with 41.70% (95% CI, 41.60%-41.80%) in the controls, corresponding to a relative risk of 0.87 (95% CI, 0.83-0.91) for acquiring COVID-19.
There was a slight, but statistically significant, difference in blood group distribution between the SARS-CoV-22 individuals and the reference population (P < .001), according to the authors.
Among the SARS-CoV-2 individuals, fewer group O individuals were found (P < .001); while more A, B, and AB individuals were seen (P < .001, P = .011, and P = .091, respectively). There was no significant difference seen among A, B, and AB blood groups (P = .30). The RR for contracting SARS-CoV-2 were 1.09 (95% CI, 1.04-1.14) for A group individuals; 1.06 (95% CI, 0.99-1.14) for B group; and 1.15 (95% CI, 1.03-1.27) for AB group, respectively.
There was no difference found in the RhD group between positive test cases and the reference population (P = .15). In addition, there was no statistical difference (all P > .40) between ABO blood groups and clinical severity of COVID-19 for nonhospitalized patients versus hospitalized patients or for deceased patients versus living patients, the researchers added.
Possible causes
The authors speculated on two possible causes of the lower prevalence of SARS-CoV-2 infection in the blood group O population. The first is that anti-A and anti-B antibodies may have an effect on neutralizing SARS-CoV viruses and that anti-A and anti-B are present on mucosal surfaces in some individuals lacking the corresponding ABO blood group. The second is that the association between ABO blood groups and levels of von Willebrand factor, which is higher in non-O individuals and is tied to an increased likelihood of arterial and venous thrombosis, could have an indirect or unknown impact on susceptibility to infection, according to the authors.
“Given the known increased risk of thrombosis in non-O individuals and the evolving central role for thrombosis in the pathogenesis of COVID-19, it is important to explore this aspect more closely in larger patient cohorts (e.g., by examining ABO blood type and viral load, the severity of symptoms, and the long-term effects following COVID-19),” the researchers concluded.
One author reported receiving fees from Bristol Myers Squibb, Novartis, and Roche. The remaining authors reported they had no competing financial interests.
SOURCE: Barnkob MB et al. Blood Adv. 2020 Oct 14. doi: 10.1182/bloodadvances.2020002657.