Q: What does blood type really mean, and is there anything to the rumor that some blood types may be at higher risk for contracting COVID-19?

A: Excellent questions. You may already know that there are four main blood types: A, B, AB, and O (with a possibility of O being either positive or negative, but I’ve not seen any studies that differentiated between them in relation to Covid-19).

In case they may help clarify ABO blood types, here are a couple of definitions:

• An antigen is any substance that causes your immune system to produce antibodies against it, because the immune system does not recognize the substance and is trying to fight it off. An antigen may be a substance from the environment, such as chemicals, bacteria, viruses, pollen, toxins, and cells from a transplanted body organ. An antigen may also form inside the body as with cancer cells. Typical an antigen triggers the immune system to produce antibodies.
• Antibodies are proteins typically produced by specialized B cells when they are triggered by an antigen. Antibodies are elite and specialized immune-system fighters that act against that specific antigen and attempt to neutralize or kill it. Think “green berets.”

Blood type is determined by the presence or absence of specific antigens named A and B, molecules that are attached to red blood cells.

• Type A: individuals with Type A have an A antigen on red blood cells and B antibodies in their plasma (the almost transparent liquid that is part of the blood).
• Type B: individuals with Type B have the B antigen on red blood cells and A antibodies in their plasma.
• Type AB: individuals with Type AB have both A and B antigens on red blood cells but neither A nor B antibodies in their plasma.
• Type O: individuals with Type O have neither A nor B antigens on their red blood cells but have both A and B antibodies in their plasma.

Now to your first question. A recent study published in the New England Journal of Medicine found that blood group O was associated with a lower risk of acquiring Covid-19 as compared with non-O blood groups. Blood group A was associated with a higher risk than non-A blood groups. researchers concluded. A potential explanation may be because the immune systems of people with Type O blood already have antibodies for both A and B in their plasma. Thus, their bodies are more equipped to identify foreign proteins—including those on the surface of viruses. Researchers do not yet know, however, if type A has an increased susceptibility to infection or to severity.

Recent studies also have shown evidence of a difference between Type A and Type B blood types. Compared with Type O, Type A seems to have a higher risk for Covid-19 related venous thromboembolism, such as pulmonary embolism and deep vein thrombosis. Again, researchers believe it is too early to link blood types definitively to outcomes.

Knowledge is power. If a person has type A blood, knowing this research could motivate them to follow recommended guidelines carefully and avoid any unnecessary exposure. In my brain’s opinion, individuals with the other blood types would be well-served to do the same.