A person’s blood type appears to have little effect on their risk of getting severely ill or dying from COVID-19, the disease caused by the SARS-CoV-2, new research shows.
The new work stands in contrast to studies conducted earlier in the pandemic that hinted that a person’s ABO blood group might play a role. Those studies may have come to that conclusion because they did not compare COVID-19 patients with appropriate controls, the authors of the new studies write.
In one new paper, Sunny Dzik and colleagues at Massachusetts General Hospital report the results of a study of 957 patients with COVID-19 admitted to that hospital and an affiliated one between mid-February and mid-May (Transfusion 2020, DOI: 10.1111/trf.15946). Of these patients, 135 died of the disease, and researchers found no association between mortality and the patients’ blood type. The researchers also compared the patients admitted to the hospital with COVID-19 with those admitted for other reasons and found no significant difference in blood group distribution, suggesting that there was no relationship between blood type and risk of getting seriously ill or dying from the disease.
Their results align with work published last month (Ann. Hematol. 2020, DOI: 10.1007/s00277-020-04169-1) by an independent group of investigators from the same hospital system. That team found that although people with type O blood seemed to be slightly less susceptible to the disease, “there was no association between ABO blood typing and what I would call severe COVID-19,” says Christopher Latz, a resident in vascular surgery at Massachusetts General Hospital who led that work.
In contrast, a nonpeer-reviewed study by Chinese investigators posted on the medRxiv preprint server in March, reported that people with blood type O had a significantly lower risk of getting COVID-19 (medRxiv 2020, DOI: 10.1101/2020.03.11.20031096). That study, Dzik and colleagues write, compared the blood group of patients with COVID-19 to “a background healthy population” instead of other, hospital patients without COVID-19, which they say is a more relevant control group.
Similarly, a genetic study of patients in Italy and Spain also found blood type O to be protective against COVID-19 (N. Engl. J. Med. 2020, DOI: 10.1056/NEJMoa2020283). Dzik and colleagues write that the study used healthy blood donors as controls, even though such a control group is “well known to be selected in favor of people in group O based on their active recruitment as preferred blood donors.”
As more research on the link between COVID-19 and blood group has emerged, the link appears to be weak, says Laura Cooling, director of immunohematology at the University of Michigan, who was not involved in any of the studies. “In the setting of widespread community infections and underlying health disparities, the role of ABO [blood groups] in COVID-19 appears minor when compared to other inherent risk factors,” she says.