If you would have asked me this question a year ago, I would have said that I think it is one of two likely answers: (1) it might, but I suspect it will be a relatively minor contribution among a whole host of factors that determine your risk, or more likely, (2) it is not actually your blood group, but rather another genetic factor determined by a gene that is in close association with the gene that determines your blood group. We have been seeing what appeared to be a correlation between your ABO blood group and risk for infection since early on in the pandemic, but we have simply not known whether that is just an association or if it is causation, and if the latter, how would your ABO blood type impact infection risk?
A recent study (Blood Group A Enhances SARS-CoV-2 Infection | Blood | American Society of Hematology (ashpublications.org)) provides us with an answer, and it appears that at least my second potential answer was wrong.
A quick refresher. Most of you will have heard of blood groups, and perhaps you are a regular blood donor and know your blood group. You also likely know that your blood group is genetically determined in that your biological family members have a limited number of possibilities for their blood group based upon your own, and you may be aware that in the past, blood group was one of the things looked at in paternity cases (it can’t prove paternity, but it can rule it out).
The prevalence of blood groups among Americans from most common to least is: O+ (roughly 38%of the population), A+, B+, O-, A-, AB+, B-, AB- (roughly 1%). The positive or negative sign that follows your ABO group is your Rh factor, and we are not going to get into that for purposes of this discussion. I qualified that these prevalence numbers are for Americans, because the prevalence of blood groups will vary among different racial and ethnic populations. Even within the U.S. population, the prevalence of blood group varies by race and ethnicity, e.g., 43% of Caucasians are blood group O, but only 28% in the Asian population, and 27% in African-Americans.
Recall that all cells have sugars (carbohydrates), proteins, or glycoproteins (sugar-protein complexes) that can be recognized by immune cells and these are called antigens. Your blood type is determined by which antigens are or are not on the cell surface of your red blood cells. However, these blood group antigens are not just present on blood cells, but other cells as well, which is why we have to seek out ABO compatible donors for various types of transplants.
Now, recall as far as the SARS-CoV-2 virus that it has a spot on its spike protein called the receptor binding domain (RBD) that attaches to the ACE-2 receptor on the host cells. The RBD binds the ACE-2 receptor beginning the process by which the virus is able to enter the cell, infects the cell, and takes over the cellular machinery that is normally used to make proteins needed by the cell, but once infected, the viral RNA gives this machinery the instructions for how to make the proteins needed for new SARS-CoV-2 progeny that are produced, assembled into a new virus and then expelled from the cell to infect other cells.
What we learn in this article is that the RBD can attach not only to the ACE-2 receptor of many of the body’s cells, but it can also bind to the carbohydrate (sugar) on the red blood cell (and other cells as well) membrane that is the antigenic determinant of blood group. And, all SARS-CoV-2 variants, including delta and omicron (and more strongly for omicron), bind most strongly and preferentially to the sugar that is associated with the A blood group. For example, SARS-CoV-2 is far more likely to infect cells that have the blood group A antigen on their surface than those that have the surface antigen associated with group O. When the virus attaches to the group A blood cell carbohydrate, the virus can enter the blood cell and can then hitch a ride to be distributed anywhere in the body that is supplied by blood, which is almost everywhere. Further, the lung cells of someone with blood group A antigen on their cell surface are far more likely to be infected than those of a person who is type O.
It is interesting that we did not see this enhanced affinity for blood group A cell infection with the original SARS virus or the other coronaviruses.
This does not mean that if you have a blood type other than A you need not worry about getting COVID. This merely gives us more information to consider as to why some people seem to be more likely to get infected than others. SARS-CoV-2 infection is far more complicated than merely your blood type.
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