Type O, Rh– blood may be linked to lower COVID-19 risks

Having O and rhesus-negative, or Rh–, blood was associated with a slightly lower risk for COVID-19 infection and severe illness or death, according to research published in Annals of Internal Medicine.

The study provides more evidence that blood type may affect risks related to COVID-19 infection and severity.

“The uncertainty around ABO or Rh blood groups and SARS-CoV-2 infection persists,” Joel G. Ray, MD, MSc, professor in the department of medicine at the University of Toronto, and colleagues wrote. “Accordingly, this population-based study was done to evaluate SARS-CoV-2 infection and severe COVID- illness in relation to ABO and Rh status.”

Ray and colleagues conducted a population-based, retrospective cohort study of adults and children in Ontario, Canada, who had their blood group assessed from 2007 through 2019 and who were later tested for SARS-CoV-2 using viral RNA polymerase chain reaction testing from mid-January through June.

They used national databases to collect information on SARS-CoV-2 tests, hospitalizations, ED visits, preexisting conditions, demographic information and income.

A total of 225,556 people who had an ABO blood group test and a SARS-CoV-2 laboratory test were included in the study. Of those, 36.3% had type A blood, 4.5% had type AB blood, 14.9% had type B blood and 44.3% had type O blood. Of participants, 13.1% had Rh– status.

Ray and colleagues determined that adjusted relative risk (aRR) for SARS-CoV-2 infection in those with type O blood was 0.88 (95% CI, 0.84-0.92; ARD = 3.9 per 1000; 95% CI, 5.4 to 2.5) compared with A, AB and B blood type.

Additionally, they found that Rh– blood types were protective against COVID-19 infection (aRR = 0.79; CI, 0.73 to 0.85; ARD = 6.8 per 1000; 95% CI, 8.9 to 4.7), with a particularly strong protection in those with O– blood (aRR = 0.74; 95% CI, 0.66-0.83; ARD = 8.2 per 1000; 95% CI, 10.8 to 5.3).

According to the researchers, those with type O blood had a lower risk for severe COVID-19 or death compared with all other blood types (aRR = 0.87; 95% CI, 0.78-0.97; ARD = 0.8 per 1000; 95% CI, 1.4 to 0.2). Compared with those who had Rh-positive blood, those with Rh– blood were also found to have a lower risk for severe COVID-19 or death (aRR = 0.82; 95% CI, 0.68-0.96; ARD = 1.1 per 1000; 95% CI, 2.0 to 0.2).

Based on the findings, Ray and colleagues concluded that type O blood may be linked to a lower risk COVID-19 infection, severe illness or death.

“At most, a small proportion of SARS-CoV-2 infection or related illness in the entire population could be prevented by some undetermined property conferred by O blood type and, perhaps, further enhanced by Rh status,” Ray and colleagues wrote. “Whether this information can influence COVID-19 prevention or treatment strategies remains to be determined.”