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Blood Type and COVID-19: What’s the Significance

If the research continues to bear out, blood type could become another risk factor to consider for COVID-19. Find out what a Canadian population-based cohort study found out about ABO and rhesus blood groups and whether some appeared to be protective against novel coronavirus infection.

TORONTO – The question of whether blood type affects likelihood of acquiring COVID-19 and severity has created a lot of buzz over the last few months.

 A new study sought to find out how the ABO and rhesus (Rh) blood groups could influence risk for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.

Results of the population-based cohort study was published in Annals of Internal Medicine. St. Michael’s Hospital researchers in Ontario, Canada, reviewed the cases of 225,556 persons adults and children, mean age 54, who had ABO blood group assessed between January 2007 and December 2019 and who subsequently had SARS-CoV-2 testing between Jan. 15 and June 30, 2020.

SARS-CoV-2 infection, determined by viral RNA polymerase chain reaction testing, was defined as the main study outcome, while the secondary outcome was severe COVID-19 illness or death. Adjusted relative risks (aRRs) and absolute risk differences (ARDs) were adjusted for demographic characteristics and comorbidities.

Results indicate that the aRR of SARS-CoV-2 infection for O blood group vs.A, AB, and B blood groups together was 0.88 (95% CI, 0.84 to 0.92; ARD, −3.9 per 1000 [CI, −5.4 to −2.5]). In addition, Rhesus-negative (Rh−) blood type was found to be protective against SARS-CoV-2 infection (aRR, 0.79 [CI, 0.73 to 0.85]; ARD, −6.8 per 1000 [CI, −8.9 to −4.7]), especially for those who were O-negative (O−) (aRR, 0.74 [CI, 0.66 to 0.83]; ARD, −8.2 per 1000 [CI, −10.8 to −5.3]).

Researchers also identified a lower risk for severe COVID-19 illness or death associated with type O blood group compared to all others (aRR, 0.87 [CI, 0.78 to 0.97]; ARD, −0.8 per 1000 [CI, −1.4 to −0.2]) and with Rh− versus Rh-positive (aRR, 0.82 [CI, 0.68 to 0.96]; ARD, −1.1 per 1000 [CI, −2.0 to −0.2]).

The authors point out that patients who rapidly died of severe COVID-19 illness may not have had SARS-CoV-2 testing.

“In this study, which was done within a universal health care system with widespread SARS-CoV-2 testing, O and Rh− blood groups were associated with a slightly lower risk for SARS-CoV-2 infection as well as severe COVID-19 illness or death,” researchers conclude.

They add, “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. Whether this information can influence COVID-19 prevention or treatment strategies remains to be determined.”