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This video is from Dr Mike Hansen's excellent medical channel, June 16, 2020. Dr Hansen works in Emergency Medicine as a pulmonary specialist and has made a number of highly informative videos on the subject of covid 19.

Transcript for the above video, originally entitled, "Does Blood Type Matter for Coronavirus (COVID-19)?."

People have either blood type A, B, AB, or O.

Are people with blood type O less prone to suffer from COVID-19? And does blood type A make people more prone to COVID-19?

Let me first start out by saying that people of all blood types can get COVID. And people with all blood types can possibly die of COVID if they get the infection.

But, based on several different studies, it looks like people with blood type O have less a chance of getting COVID-19, and people with type A might have a higher chance of getting the infection.

Data from China was the first to show the ABO blood group association with COVID-19 infections.

The researcher Zhao and others compared ABO blood groups of controls from the general population with over 2100 COVID patients from three hospitals in Wuhan.

Across all three hospitals, blood group A was associated with a higher risk for COVID compared with non-A blood groups, whereas blood group O was associated with a significantly lower risk for infection compared with non-O blood groups.

There was another observational study on data from the New York-Presbyterian hospital system, which happens to be where I did my fellowship training. So there, over 1500 people tested for COVID, and they had similar results with blood types.

There was another study done by Andre Franke in Italy and Spain.

In this study, they looked at DNA samples from 1,980 COVID-19 patients who were hospitalized for respiratory failure. And the study produced similar results.

But what about the severity of illness?

Does having blood type O, make someone less likely to have a severe illness from COVID, compared to type B, type AB, and type A?

Well, Zhao and others looked at the case fatality rate, and blood group A was linked to higher mortality risk compared to blood group O.

Interestingly, the association of blood type is not explainable by other risk factors, like obesity, diabetes, and high blood pressure.

Recently, there was a study published by the personal genetics company 23andMe regarding evidence that blood type plays a role in COVID-19.

So if you don’t know, 23andMe is a company that sends out personal genetics testing kits to individuals who are interested in finding out their genetic history and or their predisposition to certain genetically transmitted diseases.

According to their website, they did a study based on over 750,000 people.

Their preliminary results suggest that O blood type appears to be slightly less susceptible to contracting the virus.

But the big question is why?

No one really knows, but there are a lot of hypotheses.

BLOOD TYPE is determined by genetics, and the genes determine the specific proteins on the surface of the cell. These proteins, then have specific sugar molecules that are added to them. They exist in our blood cells and other cell types.

People who are blood type A carry A-sugar-antigens

People who are blood type B carry B-sugar-antigens

People with O blood type have neither A nor B-sugar antigens.

What is the significance of this?

This means that the immune systems of people with type A blood develop antibodies for B antigens.

People with type B blood type have antibodies for A antigens.

People with type O blood have antibodies for both A and B antigens.

People with AB blood type will have neither anti-A nor anti-B antibodies.

And here is an interesting fact we knew before COVID.

There are studies showing that people with type O blood have lower levels of proteins that promote blood clotting.

More specifically, people with blood group O have about 25% lower levels of von Willebrand factor (VWF) than those with types A, B, or AB. This is due to increased clearance of VWF from the circulation.

VWF is always involved in the development of clots, so if there is less VWF, there’s likely to be less clotting. So this might explain why Type O blood type means fewer blood clots, and this might at least partially explain why people with Type O overall have less severe disease. Because as you probably know already, lots of people with COVID pneumonia also have blood clots. Also, we know that the SARS-CoV-2 can replicate in cells that express blood type antigens. Such as the cells that form the lining of our lungs, and the cells that form our tiny little air sacs, the alveoli. And the cells that line the inside of our mouth and nasal passageways. This means that when an infected person coughs or sneezes, there's a possibility that they release viral particles that are coated with their blood type antigens. So this is at least a theory from some scientists.